Rex says
Everyday utility math — the kind you'd otherwise pull up four browser tabs for. I keep it to one clean answer.
Try a scenario
Click to load — tweak from there.Inputs
Result
Calculated load (amps)
106
Headroom vs your panel
94
Percent of panel capacity used
53%
Total calculated load (VA)
25,440
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One click, a permanent link with your numbers baked in.
How to use this
- 1Enter house square footage (sq ft).
- 2Enter small appliance/laundry circuits (usually 3).
- 3Enter fixed appliance load (range, dryer, water heater, etc.) (VA).
- 4Enter hvac/heat load (VA).
- 5Enter largest single motor (e.g., ac compressor) (VA).
- 6Enter existing panel size (A).
- 7Read your calculated load (amps) on the right — it updates as you type.
- 8Hit Share to keep the scenario or send it to someone.
About this calculator
Approximates the NEC Article 220 standard method for residential electrical load calculations, used by electricians to size a service panel or check whether an existing panel has room for an addition like an EV charger, heat pump, or hot tub. It applies the standard 3 VA per sq ft general lighting load, plus small appliance and laundry circuits, then applies NEC demand factors (only a portion of total connected load is counted after the first 10kVA, since not everything runs simultaneously) before adding the largest single motor load at 125%. This is a planning estimate — an actual panel upgrade or new circuit still requires a licensed electrician's calculation and permit, but it tells you quickly whether you're likely to have headroom or need a service upgrade.
Worked example
Using the values the calculator loads with:
Inputs
- House square footage: 2200 sq ft
- Small appliance/laundry circuits (usually 3): 3
- Fixed appliance load (range, dryer, water heater, etc.): 15000 VA
- HVAC/heat load: 8000 VA
- Largest single motor (e.g., AC compressor): 4000 VA
- Existing panel size: 200 A
Results
- Calculated load (amps): 106
- Headroom vs your panel: 94
- Percent of panel capacity used: 53%
- Total calculated load (VA): 25,440
What each field means
Inputs
- House square footage (sq ft)
- The house square footage used in the calculation, measured in sq ft. Starts at 2200 sq ft so you have a working example on load.
- Small appliance/laundry circuits (usually 3)
- The small appliance/laundry circuits (usually 3) used in the calculation. Starts at 3 so you have a working example on load. Accepted range: 1–6.
- Fixed appliance load (range, dryer, water heater, etc.) (VA)
- The fixed appliance load (range, dryer, water heater, etc.) used in the calculation, measured in VA. Starts at 15000 VA so you have a working example on load.
- HVAC/heat load (VA)
- The hvac/heat load used in the calculation, measured in VA. Starts at 8000 VA so you have a working example on load.
- Largest single motor (e.g., AC compressor) (VA)
- The largest single motor (e.g., ac compressor) used in the calculation, measured in VA. Starts at 4000 VA so you have a working example on load.
- Existing panel size (A)
- The existing panel size used in the calculation, measured in A. Starts at 200 A so you have a working example on load. Accepted range: 60–400 A.
Results
- Calculated load (amps)
- Returned as a whole number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Headroom vs your panel
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Percent of panel capacity used
- Returned as a percentage. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Total calculated load (VA)
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
Is this the exact calculation my electrician will use?
It's a simplified version of the NEC standard method (220.82/220.83) that captures the main components — general lighting, small appliance/laundry circuits, fixed appliances, HVAC, and the largest motor at 125%. A licensed electrician's actual permit calculation may include additional nuances (optional method, existing dwelling rules) that shift the number somewhat.
How much headroom do I need for an EV charger?
A Level 2 home charger typically draws 30-50 amps continuous, which the NEC requires be calculated at 125% of continuous load (so a 40A charger needs 50A of panel capacity accounted for). If your headroom is under that, you'll need either a load-management device, a circuit downgrade, or a full panel upgrade.
Why does the calculation not just add everything up?
Because not every circuit runs at full draw simultaneously — your dryer, oven, and AC compressor rarely all run flat-out at the same instant. NEC demand factors statistically account for this diversity, which is why the calculated load is meaningfully lower than the sum of every circuit's breaker rating.
When do I actually need a panel upgrade?
If your calculated load is within 10-15% of your panel's rated capacity, or adding a new large load (EV charger, heat pump, hot tub, workshop) would push you over it, a 200A upgrade from 100A or 150A is the common fix — budget $2,500-$5,000 depending on utility service entrance work required.
Accuracy and limitations
- Estimates assume standard, average conditions — local rules, pricing, and materials vary.
- Results are rounded for readability; add a buffer before ordering, booking, or committing.
- Double-check anything with a real cost attached against a local quote.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Whole Home Electrical Load Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/whole-home-load-calc
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/whole-home-load-calc" target="_blank" rel="noopener">Whole Home Electrical Load Calculator — RevenueLab</a> (2026).</p>
Source: [Whole Home Electrical Load Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/whole-home-load-calc) (2026).