Electrical Load Calculator
Calculate dwelling electrical load and required service size with demand factors.
About Electrical Load Calculator
Demand factors apply because connected load far exceeds simultaneous load. Heating and cooling are not added together since only the larger can run, but electric vehicle charging is treated as a continuous load at full value. Adding an electric vehicle charger is what most often pushes an existing 100 amp service over its limit, and this calculation is how that is established before the work starts.
Formula
Electrical Load
First 3,000 VA at 100 per cent, remainder of general load at 35 per cent, plus appliances and HVAC
- demand factor
- Recognition that not all loads run at once
- general lighting load
- 3 VA per square foot plus small appliance and laundry circuits
Worked example
With the default values below, Electrical Load Calculator returns Service Size Required of 113.0. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Floor areaminimum 1 m2
- 150 m2
- Fixed appliance loadminimum 0 W
- 12,000 W
- Largest of heating or cooling loadminimum 0 W
- 5,500 W
- Electric vehicle chargerminimum 0 W
- 7,400 W
- Supply voltageminimum 100 V
- 240 V
Results
- Service Size Required
- 113.0 A
- Total Calculated Demand
- 27,120 W
- General Lighting and Receptacle Load
- 9,344 W
- Recommended Panel Rating
- 125 A
- Spare Capacity at That Panel
- 9.60%
Step by step
- 1Values used
- 2Electrical Load
- 3Service Size Required= 113.0 A
- 4Total Calculated Demand= 27,120 W
- 5General Lighting and Receptacle Load= 9,344 W
- 6Recommended Panel Rating= 125 A
- 7Spare Capacity at That Panel= 9.60
Assumptions and limits
- The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Electrical Load calculated?
First 3,000 VA at 100 per cent, remainder of general load at 35 per cent, plus appliances and HVAC Demand factors apply because connected load far exceeds simultaneous load. Heating and cooling are not added together since only the larger can run, but electric vehicle charging is treated as a continuous load at full value.
Why does Electrical Load matter?
Adding an electric vehicle charger is what most often pushes an existing 100 amp service over its limit, and this calculation is how that is established before the work starts.
What values do I need to enter?
This calculator takes 5 inputs: Floor area, Fixed appliance load, Largest of heating or cooling load, Electric vehicle charger, Supply voltage. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.