Wh to mAh Conversion Guide

Introduction

Converting battery energy (watt-hours) to capacity (milliamp-hours) is essential for understanding battery specifications, comparing batteries at different voltages, and meeting airline travel regulations. Energy (Wh) and capacity (mAh) are related through voltage with an inverse relationship—higher voltage means lower mAh for the same energy. The conversion formula mAh = (Wh × 1000) / V reveals that voltage is critical—the same energy at different voltages gives different capacity values. Understanding this conversion enables engineers to properly compare batteries, understand airline carry-on limits (typically 100Wh maximum), select replacement batteries, and calculate battery capacity from energy ratings. Wh is the complete energy specification that accounts for both charge and voltage, while mAh requires voltage to be meaningful.

This guide is designed for electrical engineers, technicians, and consumers who need to convert between battery energy and capacity for battery selection, airline travel compliance, and power bank comparison. 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: Wh to mAh Conversion Formula

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

Core Formula

Where:

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

Alternative Form

Where: $Ah = \frac{Wh}{V}$

Worked Example

Reference Table

Key Standards

Important Note

Common Conversions

Understanding the Reverse Conversion

While mAh to Wh conversion is commonly needed to understand battery energy content, the reverse conversion (Wh to mAh) is equally important for:

Practical Reasons for Wh to mAh Conversion:

• Understanding how battery energy (Wh) translates to familiar capacity (mAh) ratings
• Comparing batteries specified in different units
• Meeting airline regulations (100Wh limit) and determining equivalent mAh
• Sizing replacement batteries when only Wh is specified
• Converting between different electric tension battery configurations

Key Understanding: Energy (Wh) is the complete specification - it tells you total stored energy. Capacity (mAh) depends on volt level and only tells you charge quantity. Converting from Wh to mAh requires knowing the operating potential.

Why Voltage Matters

Electric tension is the critical factor that determines how energy (Wh) translates to capacity (mAh). The relationship is inversely proportional - higher volt level means lower mAh for the same energy.

Mathematical Relationship:

From $E = Q \times V$ (energy = charge × potential):

Rearranging to solve for mAh:

Inverse Electrical potential Relationship:

• Double the V value → Half the mAh (same energy)
• Triple the electric tension → One-third the mAh (same energy)

Example: 74Wh battery at different voltages:

• 3.7V: 20,000 mAh
• 7.4V: 10,000 mAh (2$\times$ volt level = ½ mAh)
• 11.1V: 6,667 mAh (3$\times$ potential = ⅓ mAh)
• 14.8V: 5,000 mAh (4$\times$ electrical potential = ¼ mAh)

All store the same 74Wh energy but vastly different charge capacities!

The Conversion Relationship

The conversion from Wh to mAh requires dividing energy by potential, then scaling by 1000 to convert from Ah to mAh.

Essential Formulas

Wh to mAh Conversion:

Reverse Conversion (mAh to Wh):

Using Amp-hours:

Then: $mAh = Ah \times 1000$

Energy in Joules:

Worked Examples: Wh to mAh Conversion

Airline Battery Limits (100Wh Rule)

Airlines regulate lithium batteries by energy content (Wh) for safety reasons:

Regulatory Limits:

• < 100Wh: Allowed in carry-on, unlimited quantity for personal use
• 100-160Wh: Requires airline approval, maximum 2 spare batteries
• > 160Wh: Prohibited in passenger aircraft (cargo only, special handling)

Why Wh, Not mAh?

Thermal runaway risk (fire/explosion) depends on stored energy (Wh), not charge (mAh). A high-electric tension battery with lower mAh can store more energy than low-volt level battery with higher mAh.

Common Devices Under 100Wh:

Devices Requiring Approval (100-160Wh):

• Professional laptops: 90-100Wh
• Large electrical power banks: 100-160Wh
• Professional camera batteries: 140-160Wh
• Portable wattage stations: 100-160Wh

Prohibited (>160Wh):

• High-capacity drone batteries
• Large portable load stations
• Professional broadcast equipment batteries
• Industrial tool battery packs

What Are the Practical Applications of?

Laptop Battery Specifications

Modern laptops increasingly display Wh prominently because it provides complete energy specification:

Example Laptop Battery Label:

Model: ABC123 Rating: 11.1V, 5200mAh, 57.7Wh Type: Lithium-ion Configuration: 3S2P Cells: 6$\times$ 18650 (2600mAh each)

Understanding the specs:

• 11.1V: 3 cells in series (3S): $3 \times 3.7\,\text{V} = 11.1\,\text{V}$

• 5200mAh: 2 parallel strings (2P) $\times$ 2600mAh per cell: $2 \times 2600 \text{ mAh} = 5200 \text{ mAh}$

• 57.7Wh: Complete energy specification

• Verification:

  $$Wh = \frac{5200 \times 11.1}{1000} = 57.7\,\text{Wh}\ \checkmark$$

Replacement Compatibility:

When replacing laptop batteries, match:

1. Potential (must match exactly: 11.1V)
2. Physical size (must fit in laptop)
3. Connector (must be compatible)
4. Wh/mAh (higher is better for runtime, but must fit)

You can safely upgrade from 48Wh to 57.7Wh battery if electrical potential and physical size match - you'll get proportionally longer runtime.

Power Bank Comparisons

Capacity banks often list multiple capacity ratings that can be confusing:

Example Energy Bank Label:

Capacity: 20000mAh (3.7V) Energy: 74Wh USB Output: 5V/2.4A Effective 5V Capacity: ~13,300mAh

What the numbers mean:

• 20,000mAh at 3.7V: Internal battery cell capacity
• 74Wh: Actual stored energy (honest measure)
• 13,300mAh at 5V: Real output capacity you can use

Comparing Electrical power Banks:

Don't compare mAh alone! Always convert to Wh for accurate comparison.

Result: Load Bank B provides 1.4% MORE usable capacity (75Wh vs 74Wh) despite showing 25% LESS mAh! This demonstrates why Wh is the honest comparison metric - it accounts for electric tension differences.

Using Our Wh to mAh Calculator

Our Wh to mAh Calculator provides instant conversions with:

• Real-time Wh to mAh conversion with volt level input
• Reverse computation (mAh to Wh)
• Common battery potential presets (Li-ion, LiFePO4, NiMH, laptop configs)
• Airline limit checker (100Wh threshold)
• Multi-electrical potential comparison tool
• Runtime estimation with device capacity input
• Energy equivalents (joules, kilowatt-hours)

The calculator includes validation for reasonable V value ranges and provides helpful context about electric tension selection and airline regulations.

Related Tools:

• mAh to Wh Converter - Forward conversion calculator
• Battery Runtime Calculator - Detailed runtime analysis
• Energy Calculator - Compute wattage from volt level and current

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

Conclusion

Converting watt-hours (Wh) to milliamp-hours (mAh) is fundamental to understanding battery specifications, comparing batteries at different voltages, and ensuring compliance with airline regulations. The relationship between energy and capacity is governed by voltage through an inverse relationship—higher voltage means lower mAh for the same energy content.

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The Core Formula

The essential conversion formula is:

This formula reveals that voltage is the critical factor—the same energy at different voltages produces dramatically different capacity values. A 37Wh battery provides 10,000mAh at 3.7V but only 3,333mAh at 11.1V, demonstrating why voltage cannot be ignored.

Why Wh Matters More Than mAh

Watt-hours (Wh) is the universal energy metric because it accounts for both charge quantity and voltage. It provides complete information about stored energy, making it the preferred specification for:

• Battery comparison across different voltages
• Airline regulations (100Wh carry-on limit)
• Energy consumption calculations
• Runtime estimation for devices

Milliamp-hours (mAh) alone is incomplete—it only describes charge quantity and requires voltage to be meaningful. Comparing batteries by mAh without voltage context leads to incorrect conclusions.

What Are the Practical Applications of?

This conversion is essential for:

1. Battery Selection: Understanding how energy ratings translate to familiar capacity values
2. Airline Travel: Determining if batteries meet carry-on limits (100Wh maximum)
3. Power Bank Comparison: Accurately comparing capacity banks with different internal voltages
4. Replacement Batteries: Converting between Wh and mAh specifications when selecting replacements
5. Device Compatibility: Calculating how many charges a power bank provides for a device

Key Reminders

• Always use nominal voltage (3.7V for Li-ion), not maximum charge voltage (4.2V)
• For same-voltage batteries, Wh and mAh increase proportionally—either metric works
• For different-voltage batteries, always use Wh for accurate comparison
• Account for 80-90% efficiency when calculating power bank output capacity
• Check battery labels for Wh rating before airline travel—it's the regulated metric

Mastering Wh to mAh conversion enables informed battery decisions, accurate capacity comparisons, and compliance with safety regulations. The inverse voltage relationship is counterintuitive but essential—higher voltage batteries deliver the same energy with less charge, making Wh the honest comparison metric.

Key Takeaways

Essential Formula

Remember: Voltage is required—you cannot convert Wh to mAh without knowing the battery voltage.

Critical Concepts

Voltage Selection Guidelines

Critical: Never use maximum charge voltage (4.2V for Li-ion) or minimum cutoff voltage (3.0V). Always use the nominal operating voltage.

Comparison Strategy

When to Use Wh:

• Comparing batteries at different voltages
• Airline travel compliance (100Wh limit)
• Energy consumption calculations
• Power bank comparisons

When mAh Works:

• Comparing batteries at the same voltage
• Understanding charge quantity at known voltage
• Device-specific capacity ratings

Rule: If voltages differ, convert to Wh. If voltages match, either metric works proportionally.

Airline Travel Quick Reference

Remember: Airlines regulate by Wh (energy), not mAh (charge), because fire risk depends on total stored energy.

Power Bank Efficiency

When calculating actual output capacity from power banks:

• Internal voltage: 3.7V (Li-ion cells)
• Output voltage: 5V (USB standard)
• Typical efficiency: 80-90% (use 85% for estimates)
• Formula: Effective mAh = (Internal mAh × 3.7V / 5V) × 0.85

Example: 20,000mAh at 3.7V = 74Wh, but delivers ~13,300mAh effective at 5V output.

Finding Battery Voltage

Method 1: Check battery label for "Nominal Voltage" or "Rated Voltage"

Method 2: Count cells and multiply

• 2S = 7.4V (2 × 3.7V)
• 3S = 11.1V (3 × 3.7V)
• 4S = 14.8V (4 × 3.7V)

Method 3: Measure with multimeter at ~50% charge state

Method 4: Check device specifications or battery compartment

Quick Conversion Examples

These examples demonstrate how the same energy produces different mAh values at different voltages—always verify voltage when comparing capacities.

Further Learning

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

References & Standards

This guide follows established engineering principles and standards. For detailed requirements, always consult the amperage 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.