mAh to Wh Conversion Guide

Introduction

Converting battery capacity (milliamp-hours) to energy (watt-hours) is essential for understanding battery energy storage, comparing batteries at different voltages, and calculating runtime. Capacity (mAh) measures electric charge, while energy (Wh) measures actual energy stored—the total work the battery can perform. The conversion formula Wh = (mAh × V) / 1000 reveals that voltage is critical—the same capacity at different voltages stores different amounts of energy. Understanding this conversion enables engineers to properly compare batteries, calculate runtime from energy consumption, meet airline travel regulations (typically 100Wh maximum for carry-on), and understand why batteries list both mAh and Wh specifications. Wh provides true energy comparison across different battery voltages, while mAh alone does not indicate energy without knowing voltage.

This guide is designed for electrical engineers, technicians, and consumers who need to convert between battery capacity and energy for battery selection, runtime calculations, and airline travel compliance. You will learn the fundamental conversion formula, how voltage affects the relationship, practical applications for different battery types, methods for finding battery voltage, and standards for battery energy measurements.

Quick Answer: mAh to Wh Conversion Formula

Convert battery capacity (mAh) to energy (Wh) by multiplying by voltage and dividing by 1000. Voltage is critical—the same capacity at different voltages stores different amounts of energy.

Core Formula

Where:

• Wh = Energy in watt-hours
• mAh = Capacity in milliamp-hours
• $V$ = Nominal voltage (V)

Alternative Form

Where: Ah = mAh ÷ 1000

Worked Example

Reference Table

Key Standards

Important Note

Common Battery Types:

• Smartphone (3000mAh, 3.7V): 11.1 Wh
• Tablet (8000mAh, 3.7V): 29.6 Wh
• Laptop (4500mAh, 11.1V): 49.95 Wh
• Power bank (10000mAh, 3.7V): 37 Wh

Understanding mAh and Wh

Battery specifications use two different but related units to describe capacity and energy:

mAh (milliamp-hours) measures electric charge capacity - how much current the battery can supply over time. It's a measure of charge quantity, not energy. Think of mAh as the size of a water tank - it tells you volume but not how much work that water can perform.

Key characteristics:

• Independent of volt level
• 1 mAh = 0.001 Ah = 3.6 coulombs
• Indicates how long battery can supply a given current
• Example: 3000mAh can supply 300mA for 10 hours or 3000mA for 1 hour

Wh (watt-hours) measures actual energy stored - the total work the battery can perform. It accounts for both charge capacity AND potential. Think of Wh as the potential energy - it tells you how much work can actually be done.

Key characteristics:

• Depends on both capacity (mAh) and electrical potential (V)
• 1 Wh = 3600 joules
• Indicates how long battery can supply a given electrical power load
• Example: 11.1Wh can wattage 1W load for 11.1 hours or 5W load for 2.22 hours

Why Voltage Matters

Potential is the critical link between charge (mAh) and energy (Wh). Here's why electrical potential dramatically affects battery energy:

• Energy is V value-Dependent: A 5000mAh battery at 3.7V stores 18.5Wh, but the same 5000mAh at 11.1V stores 55.5Wh - three times the energy!

• Different Chemistries, Different Voltages:

  • Lithium-ion: 3.7V nominal (3.0-4.2V range)
  • Lithium Phosphate: 3.2V nominal
  • NiMH: 1.2V nominal
  • Lead-acid: 2.0V per cell (12V battery = 6 cells)

• Series vs Parallel Configurations:

  • Series (S): Adds electric tension, keeps capacity → 2S = 2x volt level, same mAh
  • Parallel (P): Adds capacity, keeps potential → 2P = 2x mAh, same electrical potential
  • Example: 3S2P pack of 2000mAh cells = 11.1V, 4000mAh, 44.4Wh

• Marketing Confusion: Load banks often advertise high mAh at internal 3.7V but deliver lower capacity at 5V USB output due to V value conversion.

The Conversion Relationship

The mathematical relationship between mAh and Wh is straightforward once volt level is known:

Fundamental Relationship: Energy = Charge $\times$ Potential

In Battery Terms: Wh = Ah $\times V = \frac{mAh}{1000} \times$ V

Essential Formulas

mAh to Wh Conversion:

Reverse Conversion (Wh to mAh):

Using Amp-hours:

Where Ah = $\frac{mAh}{1000}$

Energy in Joules:

Worked Examples: mAh to Wh Conversion

Let's work through practical examples for different battery types:

Common Battery Types

Smartphone and Tablet Batteries

Modern smartphones and tablets use single-cell lithium-ion or lithium-polymer batteries:

Typical Specifications:

V value Evolution:

• Older devices: 3.7V nominal (3.0-4.2V range)
• Modern devices: 3.8-3.85V nominal (3.0-4.35V or 4.4V range)
• Higher electric tension provides 3-5% more energy for same mAh

Laptop Batteries

Laptop batteries use multi-cell configurations for higher volt level and capacity:

Common Configurations:

2S1P (2 series, 1 parallel):

• Potential: 7.4V
• Capacity: Same as single cell
• Example: $2 \times 3000mAh$ cells = 7.4V, 3000mAh, 22.2Wh

3S1P (3 series, 1 parallel):

• Electrical potential: 11.1V
• Example: $3 \times 4000mAh$ cells = 11.1V, 4000mAh, 44.4Wh

3S2P (3 series, 2 parallel):

• V value: 11.1V
• Capacity: 2x single cell
• Example: $6 \times 2500mAh$ cells = 11.1V, 5000mAh, 55.5Wh

4S2P (4 series, 2 parallel):

• Electric tension: 14.8V
• Example: $8 \times 3000mAh$ cells = 14.8V, 6000mAh, 88.8Wh

Power Banks

Electrical power banks store energy at internal battery volt level (usually 3.7V) and boost to 5V for USB output:

Key Considerations:

1. Internal Energy: Evaluate using internal potential (3.7V)
2. Output Capacity: Lower at 5V due to electrical potential boost and losses
3. Output ratio: Typically 85-92% for quality units
4. Multiple Outputs: Some provide 5V, 9V, 12V, 20V (USB-PD)

Conversion Example:

10,000mAh wattage bank at 3.7V:

• Internal energy: 37Wh
• 5V output (90% efficient): 6,660mAh at 5V
• 9V output (90% efficient): 3,700mAh at 9V
• 12V output (90% efficient): 2,775mAh at 12V

Runtime Calculations

Measure how long a battery will load a device by dividing battery energy by device capacity consumption. This section covers both methods and real-world yield considerations.

Fundamental Formula

The basic runtime analysis is simple:

Method 1: Using Wh (Recommended)

This method works for any battery and device combination:

Method 2: Using mAh (Same V value Only)

This method only works when battery and device operate at the same electric tension:

Important: Method 2 requires matching voltages. If voltages differ, use Method 1 (Wh).

Practical Examples

Example 1: Smartphone Battery Runtime

Given:

• Battery: 15 Wh (typical smartphone)
• Device wattage: 2 W average usage

Step 1: Assess theoretical runtime

Step 2: Apply performance factor (85%)

Result: Approximately 6.4 hours of actual usage time

Example 2: Laptop Battery Runtime

Given:

• Battery: 50 Wh (typical laptop)
• Device load: 25 W typical load

Step 1: Determine theoretical runtime

Step 2: Apply effectiveness factor (85%)

Result: Approximately 1.7 hours of actual usage time

Example 3: Capacity Bank Charging Capacity

Given:

• Energy bank: 37 Wh
• Phone battery: 11 Wh

Step 1: Compute theoretical charges

Step 2: Apply productivity factor (85%)

Result: Can charge the phone approximately 3 times before the electrical power bank is depleted

Understanding Output ratio Factors

Theoretical calculations assume 100% yield, but real-world performance is typically 80-90% of theoretical. Use 0.85 (85%) as a standard multiplier for most scenarios.

Factors Affecting Performance:

Effectiveness Multipliers by Scenario:

Quick Reference: Common Device Wattage Consumption

Pro Tips for Accurate Runtime Estimates

1. Measure actual capacity consumption: Use a USB energy meter or multimeter to measure real device electrical power, as specifications often show maximum values.

2. Account for usage patterns: Wattage consumption varies significantly:

   • Screen brightness affects load draw
   • CPU/GPU intensive tasks increase consumption
   • Network activity (WiFi, cellular) adds load

3. Consider battery age: Older batteries have reduced capacity. Multiply by 0.75-0.80 for batteries with 200+ charge cycles.

4. Temperature matters: Cold environments significantly reduce battery capacity. Plan for 20-50% reduction in cold weather.

5. Use Wh for accuracy: Always convert to Wh when comparing or calculating runtime. It's the most reliable method.

Using Our mAh to Wh Calculator

Our mAh to Wh Calculator simplifies these conversions and provides:

• Instant mAh to Wh conversion with potential input
• Reverse determination (Wh to mAh)
• Common battery electrical potential presets (Li-ion, LiFePO4, NiMH, Lead-acid)
• Energy equivalents (joules, kilowatt-hours)
• Runtime estimation with capacity input
• Battery comparison tool for different voltages
• Series/parallel configuration calculator

The calculator includes validation for reasonable V value ranges and provides helpful tooltips explaining nominal vs maximum electric tension selection.

Related Tools:

• Wh to mAh Converter - Reverse conversion calculator
• Battery Life Calculator - Detailed runtime analysis
• Power Calculator - Find wattage from volt level and amp

Our calculations follow industry best practices and have been validated against real-world scenarios.

Conclusion

Converting mAh to Wh requires understanding that battery capacity (mAh) and energy storage (Wh) are related through voltage. The formula Wh = (mAh × V) / 1000 is fundamental to comparing batteries, calculating runtime, and meeting regulatory requirements. Voltage is critical—the same capacity at different voltages stores different amounts of energy. Wh provides true energy comparison across different battery voltages, while mAh alone does not indicate energy without knowing voltage. When comparing batteries at different voltages, always use Wh. When comparing same-voltage batteries, both Wh and mAh work proportionally. For airline travel, check Wh first—it's the regulated metric (typically 100Wh maximum for carry-on without approval). Always use nominal voltage from the battery specification, not maximum charge voltage.

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Key Takeaways

Core Conversion Formula

Convert mAh to Wh using the fundamental formula:

$Wh = \frac{mAh \times V}{1000}$

Critical principle: Voltage is essential—the same capacity (mAh) at different voltages stores different amounts of energy. A 5000 mAh battery at 3.7 V stores 18.5 Wh, while a 5000 mAh battery at 11.1 V stores 55.5 Wh (3× more energy).

Voltage Relationship

Direct proportionality: Energy is directly proportional to voltage for the same capacity. Doubling the voltage doubles the energy stored:

• Same mAh, different voltage: $Wh_2 = Wh_1 \times \frac{V_2}{V_1}$
• Example: 3000 mAh at 3.7 V = 11.1 Wh; at 7.4 V = 22.2 Wh (exactly double)

Voltage Selection

Use nominal voltage, not maximum charge voltage:

• Li-ion: Use 3.7 V nominal (not 4.2 V maximum charge)
• LiFePO4: Use 3.2 V nominal (not 3.6 V maximum charge)
• NiMH: Use 1.2 V nominal per cell
• Lead-acid: Use 2.0 V nominal per cell

Why nominal voltage? Nominal voltage represents the average operating voltage during discharge, providing accurate energy calculations for practical applications.

Battery Comparison

Always compare batteries using Wh, not mAh alone:

• Wh is universal: Works across all battery types and voltages
• mAh is misleading: Requires voltage to be meaningful
• Example: A 3000 mAh battery at 7.4 V (22.2 Wh) stores more energy than a 5000 mAh battery at 3.7 V (18.5 Wh), despite having lower mAh

Comparison formula:

$\text{Energy Ratio} = \frac{Wh_1}{Wh_2} = \frac{mAh_1 \times V_1}{mAh_2 \times V_2}$

Airline Travel Regulations

Check airline limits by Wh, not mAh:

• Carry-on limit: Typically 100 Wh maximum without approval
• Approval required: 100-160 Wh (varies by airline)
• Prohibited: Over 160 Wh (must be shipped as cargo)

Common examples:

• Smartphone (15-20 Wh): ✔ Allowed
• Laptop (40-60 Wh): ✔ Allowed
• Large laptop (80-100 Wh): ✔ Allowed (check airline)
• Power bank (74 Wh): ✔ Allowed

Runtime Calculations

Calculate runtime from Wh for accuracy:

$\text{Runtime (hours)} = \frac{\text{Battery Wh}}{\text{Device Power (W)}}$

Why Wh is better than mAh:

• Accounts for voltage automatically
• Works across different battery voltages
• More accurate for devices with varying current draw
• Accounts for voltage drop during discharge

Example: 55.5 Wh battery powering a 10 W device:

$\text{Runtime} = \frac{55.5 \text{ Wh}}{10 \text{ W}} = 5.55 \text{ hours}$

Finding Battery Voltage

Methods to determine battery voltage:

1. Check battery label: Look for nominal voltage specification
2. Count cells:
   • 2S (2 series) = $2 \times 3.7 \text{ V} = 7.4 \text{ V}$
   • 3S (3 series) = $3 \times 3.7 \text{ V} = 11.1 \text{ V}$
   • 4S (4 series) = $4 \times 3.7 \text{ V} = 14.8 \text{ V}$
3. Measure at 50% charge: Nominal voltage approximates mid-discharge voltage
4. Check datasheet: Manufacturer specifications provide exact values

Series and Parallel Configurations

Understanding battery pack configurations:

• Series (S): Voltages add, capacity stays same
  • Example: 3S = $3 \times 3.7 \text{ V} = 11.1 \text{ V}$, same mAh
• Parallel (P): Capacities add, voltage stays same
  • Example: 2P = $2 \times \text{mAh}$, same voltage
• Combined (3S2P): 6 cells total = 11.1 V, 2× capacity, 2× energy

Power Bank Considerations

Power banks advertise internal capacity but deliver less at output:

• Internal: Stored at 3.7 V (Li-ion)
• Output: Delivered at 5 V (USB)
• Efficiency loss: 85-92% typical conversion efficiency
• Effective capacity: Lower at 5 V due to voltage boost and losses

Always compare power banks by Wh, not mAh, as this accounts for voltage conversion and provides true energy comparison.

Further Learning

• Wh to mAh Guide - Reverse conversion from energy to capacity
• Battery Life Guide - Calculating battery runtime and energy
• Energy Consumption Guide - Understanding energy usage calculations
• Power Guide - Understanding power relationships
• mAh to Wh Calculator - Interactive calculator for battery conversion

What Are the Common Applications of?

The conversion from mAh to Wh is critical in a wide range of battery-powered applications and scenarios:

• Portable Electronics: When comparing smartphones, laptops, or tablets, converting their battery capacities from mAh to Wh provides a true energy comparison, especially if they operate at different internal voltages.
• Power Bank Sizing: Understanding the actual energy (Wh) a power bank can deliver (after accounting for internal voltage conversion and efficiency losses) helps in determining how many times it can charge a specific device.
• Drone and RC Batteries: For hobbyists and professionals, converting mAh to Wh is essential for accurately comparing battery packs with different cell configurations (e.g., 3S vs 4S LiPo) and estimating flight times.
• Electric Vehicles (EVs) and E-bikes: While larger, the principle applies. Knowing the Wh capacity of individual battery modules helps in calculating the total energy storage of the vehicle.
• Airline Travel Regulations: Many airlines impose restrictions on the total Wh of spare batteries allowed in carry-on luggage. Accurate mAh to Wh conversion is necessary to comply with these regulations.
• Off-grid Solar Systems: Sizing battery banks for solar installations requires knowing the total energy capacity in Wh to match it with the energy demand and solar panel generation.
• Wearable Devices: For smartwatches and fitness trackers, converting their small mAh capacities to Wh helps in estimating their operational lifespan between charges.

How Do You Troubleshoot?

If your mAh to Wh conversions or battery performance seems off, consider these troubleshooting steps:

• Verify Nominal Voltage: The most common error is using an incorrect voltage. Always use the nominal voltage (e.g., 3.7V for Li-ion) printed on the battery or in its datasheet, not the maximum charge voltage (e.g., 4.2V).
• Check for Multi-Cell Packs: If dealing with a battery pack, ensure you are using the total pack voltage (e.g., 11.1V for a 3S Li-ion pack), not the voltage of a single cell.
• Confirm mAh Rating: Double-check the mAh value from the battery label or specifications. Ensure it's the actual capacity and not a misprint or marketing exaggeration.
• Account for Conversion Efficiency: For devices like power banks that convert internal battery voltage to a different output voltage (e.g., 3.7V to 5V USB), remember that efficiency losses (typically 10-20%) will reduce the effective Wh output.
• Battery Age and Degradation: Over time, batteries lose capacity. If an old battery yields lower Wh than expected, it might be due to normal degradation.
• Measurement Errors: If you're measuring voltage or current, ensure your multimeter is calibrated and used correctly.
• Consult Manufacturer Data: For any discrepancies, the manufacturer's official specifications or datasheets are the most reliable source of information.

Common Mistakes

Avoid these frequent errors when converting mAh to Wh or assessing battery performance:

• Ignoring Voltage (The Biggest Mistake): Directly comparing mAh values of batteries with different nominal voltages is misleading. A 3000mAh 7.4V battery (22.2Wh) stores more energy than a 5000mAh 3.7V battery (18.5Wh). Always convert to Wh for accurate comparison.
• Using Maximum Charge Voltage: Applying the fully charged voltage (e.g., 4.2V for Li-ion) instead of the nominal voltage (3.7V) will overestimate the Wh capacity.
• Forgetting the 1000 Multiplier/Divider: Incorrectly handling the "milli" (x1000 or /1000) factor when converting between mAh and Wh/Ah is a common arithmetic error.
• Not Accounting for Conversion Losses: Especially with power banks, assuming 100% efficiency when stepping up voltage from the internal battery (e.g., 3.7V) to the output (e.g., 5V USB) leads to an overestimation of usable Wh.
• Confusing mAh for Energy: mAh is a unit of charge, not energy. While related, it does not fully describe the work a battery can do without considering its voltage.
• Misinterpreting "mAh at X Volts": Some manufacturers might list mAh at the output voltage (e.g., 5V) rather than the internal cell voltage. Clarify which voltage is being used for the mAh rating.
• Ignoring Battery Degradation: Overlooking the fact that battery capacity (and thus Wh) diminishes over its lifespan and with charge cycles. Calculations based on "new" ratings might not reflect current performance.

Advanced Design Considerations

Load Analysis Best Practices

• Diversity Factors: Not all loads operate simultaneously—apply NEC demand factors per Article 220
• Future Growth: Design for 25% expansion capacity minimum
• Load Monitoring: Install amperage monitoring for data-driven capacity planning
• Harmonics: Non-linear loads (VFDs, LED drivers) may require derating

Installation Environment

• Ambient Degree: Derate conductors per NEC 310.15(B) above 30°C (86°F)
• Altitude: Above 3,300 ft, derate equipment per manufacturer specs
• Enclosure Type: NEMA 1 (indoor) vs NEMA 3R (outdoor) affects heat dissipation
• Vibration: Industrial environments may require vibration-rated components

Code Compliance Checklist

• NEC Article 220 demand factors applied correctly
• Conductor ampacity meets NEC Table 310.15(B)(16)
• Volt level drop $\leq 3\% feeders, \leq 5\%$ total per NEC 210.19(A)
• OCPD sized per NEC 240.4 (125% continuous load minimum)
• Equipment suitable for available fault electrical flow
• Grounding and bonding per NEC Article 250

Cost Optimization Strategies

• First Cost vs Lifecycle: Higher performance may justify premium equipment
• Conductor Sizing: Oversizing reduces losses, may pay back in 3-5 years
• Modular Design: Easier future expansion, higher upfront cost
• Energy Monitoring: Submetering enables cost allocation and optimization

References & Standards

This guide follows established engineering principles and standards. For detailed requirements, always consult the amp adopted edition in your jurisdiction.

Primary Standards

IEC 61960 Secondary cells and batteries containing alkaline or other non-acid electrolytes. Defines battery energy capacity calculations and specifications for lithium-ion and other battery types.

IATA Regulations International Air Transport Association regulations for transporting batteries. Limits spare batteries in carry-on luggage to 100Wh maximum without approval. Batteries 100-160Wh require airline approval. Batteries over 160Wh are prohibited in passenger aircraft.

Supporting Standards & Guidelines

IEC 60050 - International Electrotechnical Vocabulary International standards for electrical terminology and definitions, including battery-related terms.

Further Reading

• Electrical Installation Guide - Schneider Electric - Comprehensive guide to electrical installation best practices

Note: Standards and codes are regularly updated. Always verify you're using the current adopted edition applicable to your project's location. Consult with local authorities having jurisdiction (AHJ) for specific requirements.

Disclaimer: This guide provides general technical information based on international electrical standards. Always verify calculations with applicable local electrical codes (NEC, IEC, BS 7671, etc.) and consult licensed electrical engineers or electricians for actual installations. Electrical work should only be performed by qualified professionals. Component ratings and specifications may vary by manufacturer.