CEC Part I · Section 8

Service Size Calculator

Given your home's estimated demand load, see which standard Ontario service size — 100A, 125A, 150A, 200A, or 400A — actually fits, with headroom.

1. Demand Load

Estimated Demand Load (A — use our Load Calculator if unsure)

Desired Headroom

2. Recommended Service

Ontario standard sizes

MINIMUM SERVICE SIZE

— A

HEADROOM AT THIS SIZE

— A

Note: Enter your demand load to see a recommendation.

This is an educational estimate. Actual service sizing must come from a proper CEC Section 8 load calculation completed by a licensed electrician, and any service change always requires an ESA permit.

Common Ontario service sizes, roughly explained

100A — the long-standing standard for many existing homes; can be tight once EVs, heat pumps, or electric ranges are added.
125A / 150A — a middle ground, sometimes used where 100A is outgrown but a full 200A upgrade isn't needed yet.
200A — the current standard for new construction and most major renovations, with comfortable headroom for electrification.
400A — typically reserved for very large homes or homes going fully electric with multiple EVs, heat pumps, and other major loads.