How to read your meter, panel label and appliance nameplates
Updated 2026-11-03 · Find your service size, main breaker rating, square footage and appliance nameplate watts, and how to get 12 months of peak demand from your utility.
A load calculation is only as good as the numbers you feed it. Here is where to find each one. Never remove the panel cover yourself; everything below is visible without tools.
Service size
- Main breaker: the large breaker at the top of the panel, labeled 100, 125, 150 or 200.
- Panel label: inside the door, it lists the busbar rating ("Rated 200 A max") and the number of spaces.
- No main breaker? Some older panels use a separate disconnect outside near the meter, or several main breakers ("rule of six"). Ask an electrician.
Appliance nameplates
| Appliance | Where the label is | What to read |
|---|---|---|
| Range | Inside the drawer or on the back | kW at 240 V |
| Dryer | Inside the door or on the back | Watts; use at least 5,000 |
| Water heater | Side of the tank | Element watts (often 4,500) |
| A/C or heat pump | Outdoor unit | MCA amps × 240 = VA |
| Air handler strips | Indoor unit | kW (5, 8, 10, 15) |
| EV charger | Charger label or app | Amps × 240 = VA |
If a value is unknown, our calculator uses a typical default, the same approach PNNL's panel tool takes (PNNL Building America Solution Center: electrical panel calculator for heat pump water heaters).
Square footage
Use the habitable floor area, measured from outside dimensions, excluding open porches, garages and unfinished spaces. Your property record or listing is a good start.
12-month peak demand (for 220.87)
Look in your utility account for interval or demand data, often a "Green Button" download. Find the highest kW over 12 months. If only monthly kWh totals are available, this method usually cannot be used.
Common questions
How do I know if I have 100 or 200 amp service?
Look at the main breaker at the top of the panel; the number on the handle (100, 150, 200) is usually the service rating. The panel label also lists the busbar rating, which can be higher.
Where do I find 12-month peak demand?
Many utilities show interval data in the online account (Green Button download). Look for the highest kW reading over the past year, not kWh.
Estimate only; a licensed electrician and your local authority having jurisdiction decide; not an engineering stamp.
Sources
- PNNL Building America Solution Center: electrical panel calculator for heat pump water heaters
- City of Sacramento: electrical load calculation worksheet (PDF)
- City of Campbell, CA: residential load calculation worksheet
- Intrysys: residential load calculator (220.82 / 220.87)