Electrical Load Calculator
Calculate current, power, resistance and the recommended circuit breaker size.
Last updated · View algorithm, constants and default inputs (JSON)
About this calculator
This simplified calculator relates voltage, current, power, resistance, power factor, and phase. If more than one of current, power, and resistance is entered, the values must agree or an error appears; set unused known-value fields to 0. The 125% figure is only a continuous-load arithmetic example, not a breaker recommendation or wiring instruction. Actual protection depends on load, conductor, equipment, and local code; consult a qualified electrician.
Worked example
calculated with the default values below
Voltage 120 V · Current (0 if not entered) 10 A · Power (leave 0 to calculate) 0 W · Resistance (leave 0 to calculate) 0 Ω · Supply phase Single phase · Power factor 1 Power 1,200.00 W · Current 10.000 A · Resistance 12.000 Ω · Apparent power 1,200.0 VA · Illustrative 125% current reference — not a breaker recommendation 15.0 A · Note Size the breaker at 125% of continuous load, and never exceed the cable rating
General background references
Disclaimer
These calculators give general estimates. Sizing, pricing, availability and standards vary by brand, retailer and country, so treat the output as a starting point and confirm it against the seller's or authority's own figures.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
P = V × I × pf × φ
- V
- Voltage (V)
- I
- Current (A)
- pf
- Power factor (0–1)
- φ
- Phase factor: single 1, three-phase √3 ≈ 1.732
- P
- Real power (W)
P = V × I × pf × φ. The 125% value is a simplified continuous-load example only; breaker and conductor selection require load, conductor, equipment, and local-code details. Not installation advice.
Frequently asked questions
What does the 125% current reference mean?
It multiplies the calculated current by 1.25 as a simplified continuous-load arithmetic example, then rounds up to a listed size. The displayed value is not a breaker recommendation: real protection depends on load, conductors, equipment and local code. Do not use this calculator to choose or install electrical equipment; consult a qualified electrician.