Load calculation for adding an EV charger
The calculation adds your household loads, applies a demand factor, adds heating or cooling, converts to amps and compares the answer with your service rating.
The steps
- Add general loads: 3 VA per square foot, two 1,500 VA small-appliance circuits and 1,500 VA for laundry.
- Add fixed appliances: range, dryer, water heater and others, using nameplate ratings.
- Add the EV charger at its breaker amps x 240 V x 125%.
- Count the first 8,000 VA at 100% and the remainder at 40%.
- Add the larger of cooling or heating (electric heat at 65%).
- Divide by 240 V and compare with the service rating.
Worked example
Illustrative home, not yours: 1,800 sq ft, electric range (12,000 VA), electric dryer (5,000 VA), electric water heater (4,500 VA), 2,000 VA of other fixed appliances and a 4,000 VA central A/C.
| General loads: lighting at 3 VA per sq ft, two 1,500 VA small-appliance circuits, 1,500 VA laundry, plus range, dryer, water heater and other fixed appliances, plus the charger (48 A x 240 V x 125% = 14,400 VA) | 47,800 VA |
| First 8,000 VA at 100%, the rest at 40% | 23,920 VA |
| Central A/C (or electric heat at 65%, whichever is larger) | 4,000 VA |
| Total, divided by 240 V | 116.3 A |
| Against a 100 A service | 116% (over, above 100%) |
A 48 A charger on this home reads 116% of a 100 A service. The same charger on a 200 A service reads 58%.
How Panel Check estimates it
Panel Check uses an NEC-style optional method for existing homes. It adds general loads, counts the first 8,000 VA in full and the remainder at 40%, adds the larger of cooling or heating, then divides by 240 V to get amps. An EV charger is treated as a continuous load, so its breaker size is multiplied by 125%. A result at or under 80% of the service rating reads as fits, up to 100% as tight, and above that as over. The heat pump figure is a rule of thumb; the nameplate on your equipment is the real number.
Frequently asked questions
Why 125% for the charger?
An EV charger can run continuously for hours, so the method counts it at 125% of its breaker size.
Why is only part of the load counted at full value?
Not everything runs at once. The optional method counts the first 8,000 VA fully and the remainder at 40%.
Is this the exact calculation my electrician will run?
It is similar, but your electrician may use a different method, measured data and local code amendments.
Try it on your own numbers
This is a planning estimate, not an electrical design. A licensed electrician must confirm your actual panel, wiring and local code requirements before any work. Nothing here is a guarantee of safety or code compliance.