Ohm's Law & Power
V = volts, I = amps, R = ohms, P = watts. DC or resistive (unity power factor) AC unless a power factor is entered.
The 12-formula wheel — find the quantity you need in the center, pick the formula that uses the two values you know.
Solve any two of V, I, R, P
Single- and three-phase power
kVA / kW ↔ amps
Series & parallel resistance
Formula list
| Find | Formulas |
|---|---|
| V | I×R · P÷I · √(P×R) |
| I | V÷R · P÷V · √(P÷R) |
| R | V÷I · V²÷P · P÷I² |
| P | V×I · I²×R · V²÷R |
| 1Ø power | W = V×I×PF · VA = V×I |
| 3Ø power | W = 1.732×V×I×PF · VA = 1.732×V×I |
| Amps from kVA | 1Ø: kVA×1000÷V · 3Ø: kVA×1000÷(1.732×V) |
| Amps from kW | kW×1000÷(V×PF) · 3Ø: ÷(1.732×V×PF) |
| Series R | R1 + R2 + R3 … |
| Parallel R | 1 ÷ (1/R1 + 1/R2 + …) · two: (R1×R2)÷(R1+R2) |
Reference only — not engineering, legal, or code-compliance advice. Results are estimates for qualified persons and must be verified against the NEC edition adopted where the work is done (your selected edition), manufacturer instructions, and the local AHJ. Use is subject to the Terms of Use & Disclaimer. — Morningstar Electric LLC