Electrical Load Calculator to estimate connected watts, demand-adjusted load, current in amps, recommended service capacity, and preliminary electrical project cost.
Home & Construction Calculators
Build a planning electrical load estimate from floor area, lighting load, fixed equipment, motor load, demand factor, voltage, and project costs.
This is a planning estimate, not an electrical design. A licensed electrician must verify circuits, conductor sizing, overcurrent protection, service capacity, grounding, voltage drop, and local code.
About the Electrical Load Calculator
This electrical load calculator estimates connected watts, demand-adjusted watts, current, a rounded planning capacity, and an early project cost allowance.
Formula and assumptions
Lighting load = area × watts per square foot. Connected load adds lighting, fixed appliances, and motor or HVAC load. Demand load = connected load × demand factor. Current = demand watts ÷ voltage. The recommended capacity rounds current upward to the next 5-amp planning step.
Worked example
A 1,500-ft² home with 3 W/ft² lighting, 4,500 W of fixed loads, and 3,000 W of motor load has 12,000 W connected load. At an 80% demand factor, the planning load is 9,600 W, or 40 A at 240 V. Final service and circuit design requires a professional load calculation.
Measurement checklist
- List every fixed appliance and motor.
- Use nameplate ratings where available.
- Confirm voltage and phase.
- Check continuous loads and starting currents.
Manual calculation steps
- Estimate lighting watts from area.
- Add fixed and motor loads.
- Apply a justified demand factor.
- Divide demand watts by voltage.
- Round only for planning comparison.
- Verify with code-required demand rules.
Frequently asked questions
Can this choose a breaker size?
No. Breaker and conductor sizing depends on circuit details, continuous loads, equipment ratings, installation method, and code requirements.
Why use a demand factor?
Not every connected load operates at full power at the same time, but the correct factor depends on the system and applicable rules.
Can this replace an electrician?
No. Use it only for early planning and have a qualified electrician verify the final design.
Common mistakes
- Using area alone for total electrical load.
- Ignoring motors and HVAC starting current.
- Applying an unsupported demand factor.
- Choosing a breaker from this estimate alone.