Home energy · electrical reference
Service load, 100, 150 or 200 amps?
Enter floor area, appliances and heating or cooling. The tool applies the NEC optional method for a single-family home and suggests a standard service size.
Short answer
Add 3 VA per sq ft, 3,000 VA for two small-appliance circuits, 1,500 VA for laundry and nameplate appliance loads. Count the first 10,000 VA at 100% and the rest at 40%, add the largest heating or cooling load, then divide by 240 V. A 2,000 sq ft home with 12,000 VA of appliances and a 5,000 VA A/C comes to 20,000 VA, about 83 A, so a 100 A service.
Inputs
Result
Worked example
2,000 sq ft: 6,000 VA lighting and receptacles + 3,000 VA small appliance + 1,500 VA laundry + 12,000 VA appliances = 22,500 VA. First 10,000 at 100% plus 12,500 x 40% = 15,000 VA. Add 5,000 VA of A/C: 20,000 VA / 240 V = 83.3 A, rounded up to a 100 A service. Swap in 15,000 VA of electric heat in one unit (65% = 9,750 VA, larger than the A/C) and the total is 15,000 + 9,750 = 24,750 VA, or 103 A, so the next standard rating is 110 A.
Formula, assumptions and sources
NEC 220.82(B): general load = 3 VA per sq ft (outside dimensions, excluding open porches, garages and unfinished spaces) + 1,500 VA for each of two small-appliance circuits + 1,500 VA laundry + nameplate VA of fastened-in-place and dedicated-circuit appliances. The first 10 kVA counts at 100% and the remainder at 40%. 220.82(C): add the largest of air conditioning at 100%, a heat pump with no supplemental heat at 100%, a heat pump at 100% plus supplemental electric heat at 65%, or electric space heating at 65% (three or fewer separately controlled units) or 40% (four or more). Amps = total VA / service voltage, rounded up to a standard rating. The method applies to a single-family dwelling served by a 120/240 V or 120/208 V three-wire service of 100 A or more, so results under 100 A show as 100 A. Not covered: neutral sizing, multifamily units, thermal storage, EV chargers beyond what you enter as nameplate VA, or conductor ampacity.
Table values here follow the NEC as reproduced in the sources below (editions 2008 to 2020 era); fill percentages, tables and allowances can change between editions, so confirm against the edition your jurisdiction has adopted.
Code and safety notes
This tool follows the U.S. National Electrical Code (NFPA 70). The Canadian Electrical Code (CSA C22.1) and local amendments differ in several tables and rules, so Canadian installations must be checked against the CEC and the authority having jurisdiction.
Planning aid only, not electrical advice. Electrical work can cause fire and shock; the adopted code edition, the equipment listing and a licensed electrician or inspector decide what is allowed.
FAQ
Is 100 amps enough for a house?
It can be for a smaller home without electric heat or an EV charger. Run the load: the optional method counts 3 VA per sq ft, appliances and the largest heating or cooling load, and many modern homes land near or above 100 A.
What is the 10 kVA and 40% rule?
Under the NEC optional method, the first 10 kVA of general load counts at 100% and everything above counts at 40%.
Does this include an EV charger?
Only if you add its nameplate VA to the appliance field. A 40 A charger at 240 V is 9,600 VA.
Does this follow the Canadian Electrical Code?
No. The CEC uses a different method (Rule 8-200), so Canadian homes need the CEC calculation from an electrician.