Ohm's law
V = I × R
I = V / R
P = V × I = I²R = V²/REducational reference
Electrical formulas
This reference rearranges voltage, current, resistance, real power, apparent power, energy, and transformer relationships into their common calculation forms. It uses SI units and the NIST and technical sources listed on the Sources page.
A compact reference for the stable equations used by Power Totals calculators.
Single-phase power
S = V × I
P = V × I × PFThree-phase power
S = √3 × VLL × I
P = √3 × VLL × I × PFConductor resistance
R = ρ × L / A
Vdrop = I × Rpath
Ploss = I² × RpathPower triangle
PF = P / S
Q = √(S² - P²)
φ = cos⁻¹(PF)Battery energy
Wh = V × Ah
runtime = usable Wh / load WIdeal transformer
Vp / Vs = Np / Ns = Is / IpResistor networks
Series: Req = ΣR
Parallel: 1/Req = Σ(1/R)Symbols
| Symbol | Meaning | Common unit |
|---|---|---|
| V | Voltage | volt (V) |
| I | Current | ampere (A) |
| R | Resistance | ohm (Ω) |
| P | Real power | watt (W) |
| S | Apparent power | volt-ampere (VA) |
| Q | Reactive power | volt-ampere reactive (VAR) |
| PF | Power factor | ratio, 0–1 |