Convert HP or kW to amps for DC, single-phase, or three-phase loads with efficiency and power factor, or reverse-solve horsepower and voltage.
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| Calculator Operations | Required Inputs |
|---|---|
| Convert Horsepower to Amps | Shaft power, voltage, efficiency, system and AC power factor |
| Convert Amps to Horsepower | Line current, voltage, efficiency, system and AC power factor |
HP to Amps Formula
The following operating-point formula estimates current from mechanical shaft power. The reverse modes use the same efficiency and system assumptions.
- Where A is the amps
- HP is the horsepower
- V is the volts
- η is motor efficiency as a fraction (entered as a percentage in the calculator); k = 1 for DC or single-phase AC and √3 for balanced three-phase AC
- PF is true power factor for AC; use 1 for DC
Multiply mechanical HP by 745.6998715822702 W/hp and divide by voltage, efficiency fraction, power factor and the system multiplier k. Three-phase voltage is line-to-line RMS and current is line RMS. DC omits power factor. Reverse shaft output is k × V × I × PF × η; voltage is shaft watts divided by k × I × PF × η.
| Horsepower (HP) | 1‑phase 120 V (A) | 1‑phase 240 V (A) | 3‑phase 208 V (A) | 3‑phase 230 V (A) | 3‑phase 460 V (A) |
|---|---|---|---|---|---|
| ¼ | 2.03 | 1.02 | 0.68 | 0.61 | 0.31 |
| ⅓ | 2.71 | 1.35 | 0.90 | 0.82 | 0.41 |
| ½ | 4.06 | 2.03 | 1.35 | 1.22 | 0.61 |
| ¾ | 6.09 | 3.05 | 2.03 | 1.84 | 0.92 |
| 1 | 8.12 | 4.06 | 2.71 | 2.45 | 1.22 |
| 1½ | 12.18 | 6.09 | 4.06 | 3.67 | 1.84 |
| 2 | 16.25 | 8.12 | 5.41 | 4.89 | 2.45 |
| 3 | 24.37 | 12.18 | 8.12 | 7.34 | 3.67 |
| 5 | 40.62 | 20.31 | 13.53 | 12.23 | 6.12 |
| 7½ | 60.92 | 30.46 | 20.29 | 18.35 | 9.18 |
| 10 | 81.23 | 40.62 | 27.06 | 24.47 | 12.23 |
| 15 | 121.85 | 60.92 | 40.59 | 36.70 | 18.35 |
| 20 | 162.46 | 81.23 | 54.11 | 48.94 | 24.47 |
| 25 | 203.08 | 101.54 | 67.64 | 61.17 | 30.59 |
| 30 | 243.69 | 121.85 | 81.17 | 73.41 | 36.70 |
| 40 | 324.92 | 162.46 | 108.23 | 97.88 | 48.94 |
| 50 | 406.15 | 203.08 | 135.28 | 122.34 | 61.17 |
| 60 | 487.39 | 243.69 | 162.34 | 146.81 | 73.41 |
| 75 | 609.23 | 304.62 | 202.93 | 183.52 | 91.76 |
| 100 | 812.31 | 406.15 | 270.57 | 244.69 | 122.34 |
| * Rounded to 2 decimals. Assumes motor efficiency η = 0.90 and power factor PF = 0.85. 1 mechanical HP ≈ 745.699872 W. Single‑phase: I = HP × 745.699872 / (η × PF × V). Balanced three‑phase: I = HP × 745.699872 / (η × PF × √3 × V), using line-to-line RMS voltage. | |||||
HP to Amps Definition
Horsepower measures power; amperes measure current. Shaft power alone does not determine current: voltage, efficiency, electrical system and AC power factor are required.
HP to Amps Example
How to calculate HP to Amps?
- First, determine the total horsepower.
Measure the horsepower of the engine.
- Next, determine the volts.
Use operating voltage; three-phase uses line-to-line RMS voltage.
- Next, determine the efficiency.
Calculate the efficiency.
- Next, determine the power factor.
Use operating true power factor for AC; omit it for DC.
- Finally, calculate hp to amps.
Calculate hp to amps using the formula above.
FAQ
Mechanical horsepower is a power unit equal to approximately 745.699872 watts. Metric horsepower is 735.49875 watts; amperes are units of current.
Current requires shaft power, voltage, motor efficiency and the electrical system. I = Pshaft/(k × V × PF × η), with k = √3 for balanced three-phase AC and 1 otherwise; PF = 1 for DC. Use line-to-line RMS voltage for three-phase AC.
