How to use the electrical load calculator
Enter the living area (not the garage, open porches or unfinished basement) and the number of kitchen small-appliance and laundry circuits; most houses have 2 and 1. Fill in the nameplate rating of each fixed appliance in VA (watts are close enough) and leave the rest at 0. Pick how the house is heated and enter the air conditioner or heat pump rating.
This is a planning estimate. A licensed electrician does the permit calculation, and local code editions differ.
The formula (NEC 220.82 optional method)
- General load = living area × 3 VA + 1,500 VA per small-appliance and laundry circuit + every fixed appliance’s nameplate
- Demand factor: the first 10,000 VA at 100%, the rest at 40%
- Heating and cooling: add the largest of the AC or heat pump at 100%, electric heat at 65% (fewer than four thermostats) or 40% (four or more), or a heat pump plus 65% of its backup strips
- Amps = total VA ÷ 240 V, then the next common service size
Worked example: 1,500 sq ft, electric range, dryer and water heater
- 1,500 × 3 VA = 4,500 VA; 3 circuits × 1,500 VA = 4,500 VA
- Range 12,000 + water heater 4,000 + dryer 5,000 = 21,000 VA
- General load 30,000 VA → 10,000 + 40% × 20,000 = 18,000 VA
- Heating and cooling: AC 5,000 VA at 100% against 65% × 6,000 VA electric heat = 3,900 VA → 5,000 VA
- Total 23,000 VA ÷ 240 V = 95.8 A → a 100 A service
Electrician U’s version of this example picks the electric heat (3,900 VA) and gets 21,900 VA. The optional method takes the largest of the heating and cooling loads, which is the 5,000 VA air conditioner here.
Load by house
Electric range (12,000 VA), dryer (5,000 VA), water heater (4,500 VA), dishwasher and disposal (1,800 VA), 5,000 VA air conditioner or heat pump.
| House | Gas heat | Heat pump + 10 kW strips | Heat pump + EV charger |
|---|---|---|---|
| 1,500 sq ft | 99.7 A → 100 A | 126.8 A → 150 A | 142.8 A → 150 A |
| 2,000 sq ft | 102.2 A → 125 A | 129.3 A → 150 A | 145.3 A → 150 A |
| 2,500 sq ft | 104.7 A → 125 A | 131.8 A → 150 A | 147.8 A → 150 A |
| 3,000 sq ft | 107.2 A → 125 A | 134.3 A → 150 A | 150.3 A → 200 A |
Common mistakes
- Counting heat and AC together. Only the larger one counts, except for a heat pump’s backup strips.
- Using breaker sizes instead of nameplates. A 30 A dryer breaker isn’t a 7,200 VA dryer; use the rating on the appliance label.
- Including the garage and basement. The 3 VA per sq ft applies to finished living space.
- Treating the result as a permit calculation. Your electrician confirms it with the code edition your town uses.
Frequently asked questions
What size electrical service does my house need?
Add the load with the NEC 220.82 optional method and divide by 240 V. A 2,000 sq ft house with an electric range, dryer and water heater, gas heat and a 5,000 VA air conditioner comes to 102.2 A, so a 125 A service. Switch it to a heat pump with 10 kW backup strips and it's 129.3 A, a 150 A service.
Is a 100 amp service enough?
Often, for a smaller house with gas heat. 1,500 sq ft with an electric range, dryer and water heater and central AC comes to about 96 A. Add electric heat, a heat pump or an EV charger and most homes pass 100 A.
Will an EV charger overload my panel?
A 40 A charger adds 9,600 VA. On the 2,000 sq ft gas-heated example it raises the calculated load from 102.2 A to 118.2 A; with a heat pump as well it reaches 145.3 A. Run your own numbers with the charger's rating.
Why count only the larger of heating and air conditioning?
They don't run at the same time, so the code treats them as noncoincident loads and counts only the bigger one. A heat pump with backup strips is the exception: the compressor counts in full plus 65% of the strips, because they can run together.
What is the 10 kVA demand factor?
Not everything in a house runs at once, so the optional method counts the first 10,000 VA of the general load in full and only 40% of the rest. 30,000 VA of lights, outlets and appliances becomes 10,000 + 8,000 = 18,000 VA.
Can I use this for my permit?
No. It's a planning estimate for deciding whether a panel upgrade is likely. The permit load calculation is done by your electrician or engineer with the full nameplate data, and your local code edition and inspector have the final say.
Sources
Formulas and defaults last reviewed October 30, 2026. How we check our math.