Amp Hours to Amps Calculator
Turn a battery’s amp-hour rating into the current it can supply over a given time — or work out how many amp-hours a load uses.
Amp-hours only become amps once you say over what time. Many batteries are rated over 20 hours (“C/20”).
Lead-acid batteries deliver less than their rated Ah at high currents (the Peukert effect); lithium holds close to rated capacity.
Quick answer
Amps = amp-hours ÷ hours. An Ah rating has no single amp value until you choose the time.
- 100 Ah over 20 hours = 5 A (the common C/20 rating) · over 10 h = 10 A · over 1 h = 100 A (1C)
- A 7 Ah alarm battery over 20 h = 0.35 A
- Going the other way: 15 A for 4 hours uses 60 Ah
How this conversion works
Why amp-hours need a time to become amps
An amp-hour is one amp flowing for one hour. A 100 Ah battery can, in theory, deliver 1 A for 100 hours, 10 A for 10 hours or 100 A for one hour — so “how many amps is 100 Ah?” has no single answer. Divide the capacity by the number of hours you want it to last, or multiply your load current by its running time to find the amp-hours it uses.
C-rate
The C-rate expresses current relative to capacity: 1C on a 100 Ah battery is 100 A, 0.5C is 50 A and C/20 is 5 A. Datasheets give a maximum continuous C-rate — often 0.5–1C for LiFePO₄ — and lead-acid capacity is usually quoted at C/20. Pull a lead-acid battery harder than its rating and it delivers fewer amp-hours than the label says.
Amp-hours to amps chart
| Capacity | over 1 h | over 2 h | over 5 h | over 10 h | over 20 h |
|---|---|---|---|---|---|
| 7 Ah | 7 A | 3.5 A | 1.4 A | 0.7 A | 0.35 A |
| 20 Ah | 20 A | 10 A | 4 A | 2 A | 1 A |
| 50 Ah | 50 A | 25 A | 10 A | 5 A | 2.5 A |
| 100 Ah | 100 A | 50 A | 20 A | 10 A | 5 A |
| 150 Ah | 150 A | 75 A | 30 A | 15 A | 7.5 A |
| 200 Ah | 200 A | 100 A | 40 A | 20 A | 10 A |
| 280 Ah | 280 A | 140 A | 56 A | 28 A | 14 A |
| 300 Ah | 300 A | 150 A | 60 A | 30 A | 15 A |
To see how long a battery runs a load in watts, use the battery runtime calculator.
Frequently asked questions
Divide amp-hours by the number of hours. 100 Ah over 20 hours is 5 A; over 5 hours it is 20 A.
It depends on how fast you discharge it. At the common 20-hour rating it is 5 A; it can supply 100 A for about an hour if its maximum current allows (1C), but a lead-acid battery would deliver noticeably fewer amp-hours at that rate.
It means the Ah capacity was measured while discharging over 20 hours. A 100 Ah battery at C/20 supplies 5 A for 20 hours.
10 Ah for every hour it runs. Over 8 hours a 10 A load uses 80 Ah.
Briefly, yes — current and capacity are different limits. The maximum discharge current is set by the battery's chemistry and its BMS, and is printed on the datasheet.
Electrical unit converters
- Watts to amps calculator
- Amps to watts calculator
- Watts to kilowatts calculator
- kW to kVA calculator
- Ohm's law calculator
- Ah to Wh calculator
- Ah to kWh calculator
- kWh to mAh calculator
- Watts to watt-hours calculator
- Joules to watts calculator
- HP to kW calculator
- BTU to kW calculator
- kWh to MJ calculator
- AWG to mm² calculator
Learn more
Sources & standards
Amp-hours, amps and discharge-rate (C-rate) conventions follow the SI definitions and the battery-capacity test standard below.
- NIST Special Publication 811 — Guide for the Use of the International System of Units (SI) — National Institute of Standards and Technology
Defines the watt, watt-hour, ampere and the conversion factors used on this page. - IEC 61427-1 — Secondary cells and batteries for renewable energy storage — International Electrotechnical Commission
Standardises how battery capacity (Ah) and the discharge time behind it are tested and reported.