Volts to Amps Calculator
Turn volts into amps with watts, ohms, amp-hours and hours, or kVA, for DC, single phase and three phase.
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Volts alone cannot give amps; a second quantity is needed. AC results assume a balanced load and the line-to-line voltage for three phase. The amp-hour mode gives the average current over the hours entered. Verify with your local code before sizing a breaker or wire.
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How to use the Volts to Amps Calculator
- Under “What do you know besides volts?” choose “Watts (power)”, “Ohms (resistance)”, “Amp-hours and hours” or “kVA (apparent power)”.
- For watts or kVA, pick the “Supply type”: “Single phase AC”, “Three phase AC” or “DC” (kVA works for AC only).
- Type the “Voltage (V)”. For three phase use the line-to-line voltage, for example 208 or 480. The amp-hour mode does not need a voltage.
- Enter the quantity for your mode: “Power (W)” with the “Power factor (PF)” (1 for heaters, about 0.8 to 0.9 for motors; hidden for DC), “Resistance (Ω)”, “Battery capacity or charge (Ah)” with “Time (hours)”, or “Apparent power (kVA)”.
- Read “Current (I)”, plus “Power (P)” or “Apparent power (S)” when they apply, then the formula steps, any warning and the table at other voltages or times.
The example buttons load a 1500 W heater, a 10 kW three phase motor, 12 V across 4 Ω, 100 Ah over 5 hours and a 5 kVA load at 240 V. “Copy result”, “Copy link” and “Print / save as PDF” keep the answer. Use the watts mode for a load you know in watts, such as a heater, and the ohms mode for a resistor or a coil. Use the amp-hour mode to see how many amps a battery supplies over a number of hours, and the kVA mode for a transformer or generator rating.
How do you convert volts to amps?
Use the formula that matches what you know:
| You know | Formula | Example |
|---|---|---|
| Watts, DC | I = P ÷ V | 1000 W ÷ 12 V = 83.33 A |
| Watts, single phase AC | I = P ÷ (V × PF) | 1200 W ÷ (120 V × 1) = 10 A |
| Watts, three phase AC | I = P ÷ (√3 × V × PF) | 5000 W ÷ (1.732 × 208 V × 0.9) = 15.42 A |
| Ohms | I = V ÷ R | 12 V ÷ 4 Ω = 3 A |
| Amp-hours and hours | I = Ah ÷ h | 100 Ah ÷ 5 h = 20 A |
| kVA, single phase | I = S ÷ V | 5000 VA ÷ 240 V = 20.83 A |
| kVA, three phase | I = S ÷ (√3 × V) | 75000 VA ÷ (1.732 × 480 V) = 90.21 A |
How do you convert volts and ohms to amps?
Ohm’s law gives the current as the voltage divided by the resistance. A 12 V supply across a 4 Ω resistor passes 3 A and dissipates 36 W (P = V × I). The same 12 Ω load at 120 V draws 10 A and 1200 W. This is exact for DC and for resistive AC loads such as heaters. For a coil or motor, use the watts mode with a power factor instead.
How do you convert amp-hours to amps?
Divide the amp-hours by the time they are drawn over. A 100 Ah battery drained over 5 hours supplies an average of 20 A; over 20 hours it supplies 5 A. The result is an average: a real battery gives less capacity at a high current (the Peukert effect). To see how long a battery lasts at a given load, use the battery runtime calculator.
How many amps is 1200 watts at 120 volts and at 240 volts?
1200 W at 120 V is 10 A, and at 240 V it is 5 A (power factor 1). At a given power, a higher voltage draws less current. The table in the tool lists the same load at 120, 208, 240, 277, 480 and 600 V for single phase.
How many amps is 75 kVA at 480 volts?
For three phase, 75 kVA at 480 V line-to-line is 75000 ÷ (1.732 × 480) = 90.21 A. At 208 V the same transformer rating is 208.18 A. Use the kVA to amps calculator when you also need the breaker size.
Worked examples
| Input | Result |
|---|---|
| 1200 W at 120 V | 10 A |
| 10000 W at 480 V | 14.15 A |
| 120 V across 12 Ω | 10 A |
| 100 Ah over 5 h | 20 A |
| 5 kVA at 240 V | 20.83 A |
Calculated by the tool above; open it with the same values to see each step.
Questions, briefly answered
Can you convert volts to amps with only volts?
No. Volts and amps measure different things, so you need a second quantity: watts, ohms, amp-hours with hours, or kVA.
What is the formula for volts to amps?
With watts it is amps = watts ÷ volts for DC, and watts ÷ (volts × power factor) for AC. With ohms it is amps = volts ÷ ohms.
How do I convert volts to amps for a three phase load?
Divide the watts by √3 × the line-to-line voltage × the power factor. 10 kW at 480 V and PF 0.85 is 14.15 A. For kVA, divide the VA by √3 × the voltage.
How many amps is 12 volts?
It depends on the load. 12 V across 4 Ω is 3 A. A 1000 W load on 12 V DC is 83.33 A, which needs heavy cable (see the battery cable size calculator).
How do I convert Ah to amps?
Divide the amp-hours by the hours: 100 Ah over 5 hours is 20 A. This is the average current, not a rated maximum.
Does the power factor matter?
For AC motors and other inductive loads, yes: a lower power factor means more amps for the same watts. Use 1 for heaters and resistive loads. DC has no power factor.
Should I size a breaker from this current?
Use the current as the starting point, then size the breaker and wire with the watts to amps calculator (next standard breaker) and the wire size calculator.