What is this ampere to kW tool used for?
This tool estimates power from a measured or field-read line current for single-phase, three-phase and DC systems.
It is useful for estimating the power of an existing feeder, load-balancing checks and first-pass generator or UPS sizing.
Formulas used
- Single-phase: P = V x I x cos phi x eta
- Three-phase: P = sqrt(3) x V x I x cos phi x eta
- DC: P = V x I x eta
Variables and meaning
- I
- Measured or entered line current.
- V
- Line voltage or system voltage level.
- cos phi
- Power factor used in AC systems to relate active power to apparent power.
- eta
- Efficiency factor; include it when converting current into output power.
- P
- Calculated approximate power.
Unit reference tables
Current units
| Unit name | Symbol | SI equivalent | Typical use |
|---|---|---|---|
| Milliampere (mA) | mA | 0.001 A | Electronic circuit currents |
| Ampere (A) | A | 1 A | Base SI current unit |
| Kiloampere (kA) | kA | 1,000 A | Industrial power systems |
Voltage units
| Unit name | Symbol | SI equivalent | Typical use |
|---|---|---|---|
| Millivolt (mV) | mV | 0.001 V | Sensors and low-level signals |
| Volt (V) | V | 1 V | Base SI voltage unit |
| Kilovolt (kV) | kV | 1,000 V | High-voltage transmission |
Power units
| Unit name | Symbol | SI equivalent | Typical use |
|---|---|---|---|
| Watt (W) | W | 1 W | Base SI heat-transfer-rate unit |
| Kilowatt (kW) | kW | 1,000 W | Larger heat loads |
| Megawatt (MW) | MW | 1,000,000 W | Very large heat-transfer rates |
| Kilocalorie per hour (kcal/h) | kcal/h | 1.16222222222 W | Legacy heat-load and process calculations |
| Btu per hour (Btu/h) | Btu/h | 0.293071070172 W | HVAC and Imperial/US heat loads |
Worked examples
9.59 A, 400 V, three-phase, 0.9 power factor and 92 efficiency
P = 1.732 x 400 x 9.59 x 0.9 x 0.92 which gives about 5.5 kW. This is the reverse of the matching kW to Ampere example.
9.15 A, 230 V single-phase, 0.95 power factor and 100 efficiency
P = 230 x 9.15 x 0.95 which gives about 2 kW.
Typical applications
- Power estimate of an existing feeder in the field
- Load balancing and panel checks
- Generator or UPS planning
- Quick power checks from meter or clamp-ammeter readings
Assumptions and limitations
- This tool gives an approximate power and does not include harmonics, starting current, ambient-temperature effects or measurement tolerances.
- In the three-phase mode, the voltage input is interpreted as line-to-line voltage.
- If the entered current already represents electrical input current, set efficiency to 1 or 100.