Circuit load calculator

Can this circuit hold what you want to plug in?

A circuit load calculator tells you whether the appliances on one 120-volt breaker fit. It does not inspect the panel, and it does not say the wiring in the wall is sound. A 15-amp breaker sounds like it has 15 amps to give. Under the usual continuous-load rule it is full at 12 amps, because a load that can run for hours is counted at 125 percent and the breaker is held to 80 percent. A 20-amp circuit is full at 16 amps on the same rule.

Check the box next to each thing that would run on this one circuit, not everything in the house. A refrigerator at 700 watts and a window air conditioner at 1,200 watts are both continuous: they can run for hours, so each is counted at 125 percent. A microwave at 1,100 watts and a hair dryer at 1,800 watts are not, because you use them and stop. A space heater at 1,500 watts is continuous, and it is the appliance that most often overloads a bedroom circuit. Lighting on the same circuit is included at 240 watts as a stand-in, not a fixture count.

How the amps are calculated

Watts divided by 120 is amps, after the 125 percent bump on anything that runs for hours. A fridge and a window unit together are already (700 × 1.25 + 1,200 × 1.25) = 2,375 watts, or about 19.8 amps. That does not fit a 15-amp or a 20-amp circuit. A fridge and the lights do: 700 × 1.25 + 240 = 1,115 watts, about 9.3 amps, which still fits a 15-amp circuit. The line under the result says which of those worlds you are in.

The panel amps are not this circuit

The panel size in the bar — 60, 100, 150, 200 — is the whole house. A 200-amp panel can still have a full 15-amp bedroom circuit. Do not add a space heater because the main breaker looks large. If this calculator says to split the loads, that means a second circuit, not a bigger number on the same outlet. A new dedicated 20-amp circuit has its own price on the small-jobs page. A panel upgrade is a different price again, and it is an owner's project.

What this will not tell you

It will not find aluminum wiring, a warm outlet, a Federal Pacific panel, or a breaker that trips for a loose neutral. Those are reasons to stop and call an electrician, not to finish the math. Nameplate watts vary. If your heater says 1,500 and this preset says 1,500, you are in the right neighborhood. If your unit says 900, trust the label. Shared kitchen circuits are often already dedicated. Do not add a heater to a kitchen small-appliance circuit because the calculator had room in the abstract.

If you rent, you can usually decide what to plug in. You usually cannot add a circuit. Use the result to stop stacking a heater on a window unit, and to ask for a dedicated circuit if the lease says the landlord handles electrical work. Reviewed as a method on 2026-09-01.

Write the result down before you buy the appliance. If the line says the circuit is full, the next price you need is a dedicated 20-amp circuit, which is on the small-jobs calculator, not a larger plug adapter. Adapters do not add amps. A power strip does not add amps either.