Amps to Amp Hours (A to Ah) Conversion Calculator

Amps to Amp Hours Calculator

Convert current (Amps) to battery capacity (Amp Hours) using time duration

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Key Formula: Amp Hours = Current (Amps) × Time (Hours). This tells you how much charge your battery can store or how long it will last at a given current draw.
Quick Presets (Common Scenarios):
Hours
Add Multiple Devices to Calculate Total Load:
▼ Advanced Options (Temperature, DoD, Voltage)
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Battery Chemistry Quick Select:
🔋 Lead-Acid
DoD: 50% | k: 1.2
🔋 AGM
DoD: 50% | k: 1.15
⚡ LiFePO4
DoD: 80% | k: 1.08
⚡ Li-ion
DoD: 90% | k: 1.05
Battery Capacity
0 Ah
= 0 mAh = 0 Wh (at 12V)
Calculation Steps
⚡ Energy Equivalents
🔋 Battery Size Guide
🌡️ Temperature Effect
Capacity at 25°C: 100%
At 0°C: ~80%
At -20°C: ~50%
⏱️ Peukert Effect
Higher discharge rates reduce effective capacity. Use Peukert mode for accurate runtime.
Multi-Device Load Summary
Amps to Amp Hours (A to Ah) Conversion Calculator
Table of Contents

How to Convert Amps to Amp Hours

Amps (A) and Amp Hours (Ah) measure different aspects of electricity. Amps measure the rate of current flow at any instant, while Amp Hours measure the total charge transferred over time. Converting between them requires knowing how long the current flows.

Think of it like water flow: Amps are like gallons per minute, while Amp Hours are like total gallons used. A 10 Amp current flowing for 2 hours delivers the same total charge as a 5 Amp current flowing for 4 hours—both equal 20 Amp Hours.

The Amps to Amp Hours Formula

Primary Formula
Ah = A × t
Ah Amp Hours (capacity)
A Current (Amps)
t Time (Hours)

This formula is fundamental to battery sizing and electrical engineering. According to Wikipedia’s article on Ampere-hour, the Ah rating indicates how much charge a battery can store or deliver before needing recharge.

Find Current from Capacity
A = Ah ÷ t
Find Runtime from Capacity
t = Ah ÷ A
Convert Ah to Watt Hours
Wh = Ah × V
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Pro Tip: When sizing batteries, add 20-30% extra capacity to account for efficiency losses and to avoid deep discharge, which shortens battery life. For solar systems, size for 2-3 days of autonomy. Use our Ah to Wh Calculator to convert to energy units.

Step-by-Step Calculation Examples

Example 1: Calculate battery capacity needed
A camping light draws 2 Amps. You need it to run for 10 hours. What battery capacity do you need?

Solution

Given: Current = 2 A, Time = 10 hours
Formula: Ah = A × t
Calculate: Ah = 2 × 10 = 20 Ah
With 25% safety margin: 20 × 1.25 = 25 Ah battery recommended

Example 2: Calculate maximum current draw
A 100 Ah battery needs to last 8 hours. What’s the maximum current it can supply?

Solution

Given: Capacity = 100 Ah, Time = 8 hours
Formula: A = Ah ÷ t
Calculate: A = 100 ÷ 8 = 12.5 A

Common Battery Capacities Reference

Battery TypeTypical CapacityVoltageCommon Uses
AA Battery2,500 mAh1.5VRemote controls, flashlights
Smartphone3,000-5,000 mAh3.7VMobile devices
Laptop Battery4,000-8,000 mAh10.8-14.4VPortable computers
Power Bank10,000-26,800 mAh3.7VDevice charging
Car Battery45-100 Ah12VVehicle starting
Deep Cycle100-400 Ah12VRV, solar, marine
EV Battery40-100 kWh*300-800VElectric vehicles

*EV batteries are typically rated in kWh (energy) rather than Ah. To convert, use Ah = kWh × 1000 ÷ V. For more electrical calculations, try our Amps to Watts Calculator.

C-Rate and Discharge Time

The C-rate describes how fast a battery charges or discharges relative to its capacity. A 1C rate means the battery fully discharges in 1 hour; 0.5C means 2 hours; 2C means 30 minutes.

C-RateCurrent (100Ah Battery)Discharge TimeApplication
0.05C5 A20 hoursRated capacity testing
0.1C10 A10 hoursNormal use
0.2C20 A5 hoursModerate load
0.5C50 A2 hoursHigh load
1C100 A1 hourFast discharge
2C200 A30 minutesPower tools, EVs
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Important: Battery capacity decreases at higher discharge rates due to internal resistance. A battery rated at 100Ah at 0.05C (20-hour rate) might only deliver 80Ah at 1C. Always check the manufacturer’s specifications for your specific discharge rate.

The Peukert Effect

The Peukert Effect is a phenomenon where battery capacity decreases as discharge rate increases. A 100Ah battery rated at a 20-hour discharge rate (5A) might only deliver 80Ah when discharged at a 2-hour rate (50A). This is especially important for lead-acid batteries.

Peukert’s Law
t = H × (C / (I × H))^k
t Actual runtime (hours)
H Rated hour rate (usually 20h)
C Rated capacity (Ah)
I Discharge current (A)
k Peukert exponent (1.0-1.4)

Peukert Exponent by Battery Type

Battery ChemistryPeukert Exponent (k)Recommended DoDCycle Life
Lithium-ion (Li-ion)1.02 – 1.0880-90%500-1000+
LiFePO4 (LFP)1.05 – 1.1080%2000-5000+
AGM Lead-Acid1.10 – 1.2050%400-800
Flooded Lead-Acid1.15 – 1.2550%300-500
Gel Lead-Acid1.20 – 1.3550%500-1000
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Pro Tip: Lithium batteries have Peukert exponents close to 1.0, meaning they deliver nearly rated capacity regardless of discharge rate. This makes them ideal for high-current applications like power tools and EVs. For more power calculations, use our Amps to Kilowatts Calculator.

Temperature Effects on Battery Capacity

Battery capacity is significantly affected by temperature. Cold temperatures slow down chemical reactions, reducing capacity. Hot temperatures can increase short-term capacity but damage the battery long-term.

TemperatureLead-Acid CapacityLithium-ion CapacityNotes
40°C (104°F)102%100%Slightly increased but reduces lifespan
25°C (77°F)100%100%Optimal operating temperature
0°C (32°F)75-85%80-90%Noticeable capacity reduction
-20°C (-4°F)50-60%60-70%Severe reduction, charging risky
-40°C (-40°F)30-40%LimitedMost batteries struggle

Frequently Asked Questions

Q1 What is the difference between Amps and Amp Hours?
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Amps (A) measure the rate of current flow at any instant—like speedometer reading. Amp Hours (Ah) measure total charge transferred over time—like odometer reading. A device drawing 5 Amps for 2 hours uses 10 Amp Hours total. The relationship is: Ah = A × hours.
Q2 How do I calculate how long a battery will last?
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Divide battery capacity (Ah) by current draw (A): Runtime = Ah ÷ A. For example, a 100Ah battery powering a 5A load lasts: 100 ÷ 5 = 20 hours. For safety, multiply by 0.8 to avoid deep discharge: 20 × 0.8 = 16 hours practical runtime.
Q3 What’s the difference between mAh and Ah?
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mAh (milliamp-hours) is 1/1000 of an Ah. To convert: 1 Ah = 1,000 mAh. Small batteries (phones, AA) are rated in mAh because the numbers are more practical. Large batteries (cars, solar systems) use Ah. A 5,000 mAh phone battery = 5 Ah.
Q4 How do I convert Amp Hours to Watt Hours?
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Multiply Amp Hours by voltage: Wh = Ah × V. For example, a 100Ah 12V battery stores: 100 × 12 = 1,200 Wh = 1.2 kWh. This is important when comparing batteries of different voltages—they might have the same Ah but different energy capacity.
Q5 Why does my battery not last as long as calculated?
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Several factors reduce actual runtime: (1) Peukert effect—higher currents reduce capacity; (2) Temperature—cold reduces capacity up to 50%; (3) Battery age—capacity degrades over time; (4) Depth of discharge—stopping at 50% doubles battery life; (5) Inverter efficiency—adds 10-15% losses.
Q6 What size battery do I need for my solar system?
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Calculate daily energy use (Wh), divide by voltage to get Ah, multiply by days of autonomy (usually 2-3), then divide by depth of discharge (0.5 for lead-acid, 0.8 for lithium). Example: 1,000Wh/day ÷ 12V × 2 days ÷ 0.5 = 333Ah of 12V batteries needed.
Related Electrical Calculators
Amp Hours to Amps Calculator Ah to Watt Hours Calculator Amps to Watts Calculator mAh to Ah Converter Amps to Kilowatts Calculator
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Author

  • Manish Kumar

    Manish holds a B.Tech in Electrical and Electronics Engineering (EEE) and an M.Tech in Power Systems, with over 10 years of experience in Metro Rail Systems, specializing in advanced rail infrastructure.

    He is also a NASM-certified fitness and nutrition coach with more than a decade of experience in weightlifting and fat loss coaching. With expertise in gym-based training, lifting techniques, and biomechanics, Manish combines his technical mindset with his passion for fitness.

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