Electrical Formulas & Conversion Guide

Accurate calculations are essential for designing and troubleshooting electrical systems. Use the following formulas to convert power, determine current draw, and apply Ohm’s Law in various electrical applications.

Power Conversion

• Watts to BTUs:
  BTUs = Watts × 3.413

• BTUs to Watts:
  Watts = BTUs ÷ 3.413

Electrical Power Formulas

Resistive Loads

• Single-Phase (Resistive):
  Watts = Volts × Amps

• Three-Phase (Resistive):
  Watts = (V1 × A1 + V2 × A2 + V3 × A3) ÷ 1.732
  (1.732 is the square root of 3)

Inductive Loads (Motors)

• Single-Phase (Inductive):
  Watts = Volts × Amps × Power Factor

• Three-Phase (Inductive):
  Watts = [(V1 × A1 + V2 × A2 + V3 × A3) ÷ 1.732] × Power Factor

Ohm’s Law

Ohm’s Law is fundamental in all electrical calculations:

• Ohms (R) = Volts ÷ Amps → R = E / I

• Amps (I) = Volts ÷ Ohms → I = E / R

• Volts (E) = Amps × Ohms → E = I × R

Kilowatts to Amps Conversion

DC Circuits

Amps = (1000 × Kilowatts) ÷ Volts
This formula converts DC kilowatts into current in amps.

AC Circuits

Single-Phase AC

Amps = (1000 × Kilowatts) ÷ (Power Factor × Volts)

• Suitable for residential and light commercial loads.

• Be sure to use the correct Power Factor (PF) (typically between 0.8–1.0).

Three-Phase AC

Amps = (1000 × Kilowatts) ÷ (√3 × Power Factor × Line Voltage)
√3 ≈ 1.732

• Used in industrial and commercial applications.

• Line-to-line RMS voltage must be used.

Quick Reference Table