Ampere (A) to Ampere-hour (Ah) Calculator
Use this calculator to convert current (amps) and runtime into battery capacity (ampere-hours).
What does “ampere to ampere-hour” mean?
An ampere (A) is a measure of current: how fast electricity is flowing at a given moment. An ampere-hour (Ah) is a measure of charge capacity over time. In plain terms, Ah tells you how much current can be delivered for how long.
You cannot convert amps to ampere-hours without a time value. Time is the missing piece. That is why this calculator asks for both current and duration.
The core conversion formula
Use this simple relationship:
- Ah = ampere-hours (battery capacity)
- A = current in amps
- h = time in hours
If time is in minutes or seconds, convert it to hours first. For example:
- 30 minutes = 0.5 hours
- 90 minutes = 1.5 hours
- 3600 seconds = 1 hour
Quick examples
Example 1: Small DC load
A load draws 2 A for 5 hours: Ah = 2 × 5 = 10 Ah. So you need at least 10 Ah, and usually more after applying a safety margin.
Example 2: Runtime in minutes
A device uses 8 A for 45 minutes. First convert 45 minutes to hours: 45/60 = 0.75 hours. Then: Ah = 8 × 0.75 = 6 Ah.
Example 3: Continuous 24-hour load
A system draws 0.8 A continuously for 24 hours: Ah = 0.8 × 24 = 19.2 Ah.
Reference table
| Current (A) | Time | Calculated Ah |
|---|---|---|
| 1 A | 10 h | 10 Ah |
| 3 A | 4 h | 12 Ah |
| 5 A | 2.5 h | 12.5 Ah |
| 12 A | 30 min | 6 Ah |
| 0.5 A | 48 h | 24 Ah |
Why add a safety factor?
Real battery performance depends on temperature, age, discharge rate, and inverter/charger losses. A practical design often adds margin:
- 110%–125% for mild conditions
- 125%–150% for cold weather or critical backup systems
This page includes a safety-factor field so you can instantly see both the theoretical Ah and a recommended Ah.
Common mistakes to avoid
- Ignoring time: amps alone do not determine capacity.
- Mixing units: minutes must be converted to hours for the formula.
- No reserve margin: exact Ah can be too tight in real-world use.
- Confusing Ah and Wh: watt-hours include voltage; Ah does not.
Ah vs mAh
Many small electronics use milliamp-hours (mAh). The conversion is:
So if your result is 2.4 Ah, that equals 2400 mAh.
FAQ
Can I convert amps to Ah without time?
No. You must know how long the current flows.
Is a higher Ah battery always better?
Higher Ah gives more runtime, but size, weight, charging rate, and budget also matter.
Does voltage affect this specific conversion?
Not directly for A to Ah. Voltage matters when converting to energy (Wh), where: Wh = V × Ah.