kW, kVA, Amps & Power Factor Calculator
Free · works offline · no account · NEC 2023 tables
Enter the voltage and any two of kW, kVA, amps or power factor and OhmBase solves the rest, including reactive kVAR. A second block converts watts, BTU per hour, tons of cooling and horsepower in one tap.
Open the free calculator →How the math works
Apparent power kVA = V × A ÷ 1,000 for single phase, or V × A × 1.732 ÷ 1,000 for three phase. Real power kW = kVA × PF, and reactive power kVAR = √(kVA² − kW²). For heat and mechanical units: 1 W = 3.412 BTU/h, 1 ton of cooling = 12,000 BTU/h, and 1 hp = 746 W.
Worked example
480 V three phase · 50 kW · power factor 0.8
- kVA = 50 ÷ 0.8 = 62.5 kVA
- Amps = 62,500 ÷ (480 × 1.732) = 75.2 A
- kVAR = √(62.5² − 50²) = 37.5 kVAR
FAQ
- Why do I need power factor?
- Amps follow apparent power (kVA), not real power (kW). Motors and transformers draw more current than their kW suggests; PF is the ratio between the two. Resistive loads such as heat have a PF of 1.
- How many watts is a ton of air conditioning?
- One ton of cooling is 12,000 BTU/h, which is about 3,517 W of heat removed — not the electrical draw of the unit. Use the nameplate for the electrical load.