Electrical Load Calculator
The NEC 220 service ladder — general lighting, appliances, demand factors — to amps and the next standard service, with the optional method beside it.
Electrical Load Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Single-family dwellings — multi-family is a different article.
- Screen-level: no EV charger field (add it to fixed loads).
- No panel-level subtotals or feeder splits.
In short: A 2,000-ft² house: 10,500 VA of general load drops to 5,625 at the 3,000/35% demand step; range 8,000; four fixed appliances at 75% = 5,625; dryer 5,000; the larger of heat and AC = 5,500; largest motor +250 — 30,000 VA total = 125.0 A exactly → a 125 A service. The 220.82 optional method on the same house: 21,000 VA = 87.5 A → 100 A.
Formula
general = 3 × ft² + 2 × 1,500 + 1,500
demand: first 3,000 VA @100%, remainder @35%
range → 8 kW (one range ≤ 12 kW); 4+ fixed appliances × 75%
amps = VA ÷ 240; service = next standard ≥ amps, min 100
[('3 VA/ft²', 'NEC general lighting, Table 220.12'), ('3,000 / 35%', 'the general-load demand step, 220.42'), ('220.60', 'heat or AC — the larger, never both'), ('+25%', 'largest motor adder, 220.50')]
Worked Example
- Multiply living area by 3 VA; add the two small-appliance and laundry circuits.
- Apply 3,000/35%; set range at 8 kW; 75% on 4+ fixed appliances.
- Keep the larger of heat and cooling; add 25% of the largest motor.
- Divide by 240; round up to the standard service.
- Re-run with the optional method; expect lower.
2,000 ft²: 5,625 + 8,000 + 5,625 + 5,000 + 5,500 + 250 = 30,000 VA = 125.0 A → 125 A service. Optional method: 37,500 connected → 21,000 VA = 87.5 A → 100 A.
Strengths & Limits Of This Model
Where this engine is strong
- The full 220 ladder computed, in order, with names
- Standard AND optional methods side by side
- The 100-A floor and EV trigger on the service card
Where it stops
- No neutral or grounding sizing
- Screen, not a stamped calculation
Practical Use Cases
Panel upgrades
100 vs 200 A, decided by arithmetic.
Additions
Does the service carry the new load?
EV readiness
The 150→200 A trigger, quantified.
Permit prep
The standard-method number inspectors ask for.
Remodels
Demand load before adding circuits.
Methodology & Editorial Standards
The NEC 220 standard method verbatim: 3 VA/ft² + 4,500 VA of circuits, demanded at 3,000/35%; range 8 kW when nameplate ≤ 12 kW; fixed appliances × 75% at 4+; the larger of heat/AC; +25% largest motor. Amps = VA ÷ 240, service = next standard ≥ amps with the 100-A dwelling floor. The 220.82 optional method (10 kVA/40%) computes on the same inputs as a comparison card. Nonpositive area and negative loads refused; areas past 20,000 ft² refused as commercial.
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Electrical Load Calculator — 8 Expert FAQs
8 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
How many watts per square foot for residential load calcs?
Three VA per square foot of living area — the NEC general lighting minimum (Table 220.12) — plus two 1,500-VA small-appliance circuits and a 1,500-VA laundry circuit before any appliance is counted.
What is the demand factor on general lighting?
The first 3,000 VA counts at 100%, everything above it at 35% — nobody runs every light at once, and the code prices that diversity in.
How is an electric range counted?
One range up to 12 kW nameplate counts as 8 kW — Table 220.55's oldest courtesy. Above 12 kW the table's columns add back; this page takes your nameplate.
Why do my appliances only count 75%?
Four or more fixed appliances (water heater, dishwasher, microwave, disposal…) get the 220.53 75% rule — they rarely run together. Fewer than four count at full nameplate.
Do heat and AC both count?
Never both — 220.60 takes the larger of the two, since they do not run in the same hour. The largest motor still adds its 25% starting allowance on top.
What size service does a house need?
Demand VA ÷ 240, rounded up to a standard rating: 100, 125, 150, 175, 200 A — never below 100 A for a dwelling. The canonical house here lands exactly on 125.
Where does an EV charger fit in the load calc?
As a fixed appliance at full nameplate — 40-80 A of continuous load. Because it runs for hours, the 125% continuous rule sizes its circuit on the Wire Size page, and it is the classic reason a 100-A service becomes a 200-A upgrade.
Why does the optional method give a smaller service?
220.82 applies one blunt factor — first 10 kVA at 100%, the rest at 40% — to everything at nameplate. It usually lands 20-30% under the standard method; jurisdictions accept one or the other, not whichever is smaller.