What Size Electrical Panel Do I Need?
A simple, educational estimator to help Ontario homeowners understand how panel sizing relates to household electrical load.
Updated 2026‑04‑22
Understanding Electrical Panel Capacity
Your home’s electrical panel (also called a service panel or breaker panel) determines how much electrical load your home can safely support at one time. Common residential panel sizes in Ontario include:
- 100‑amp service — older homes, limited expansion room
- 125‑amp service — moderate capacity
- 150‑amp service — mid‑range modern homes
- 200‑amp service — standard for many newer homes
- 300‑amp or 400‑amp service — large homes or homes with high‑demand equipment
Panel size affects what you can add to your home — EV chargers, heat pumps, hot tubs, induction stoves, or additional circuits. This estimator provides a rough idea of the panel size that may be required based on your expected peak load.
This tool is educational only. Real electrical design must be performed by a licensed electrician who can evaluate wiring, service entrance capacity, grounding, and local code requirements.
Panel Size Estimator
Educational only. Always consult a licensed electrician.
How to Estimate Your Peak Load
Your home’s peak load is the maximum amount of electricity used at one time. Examples of high‑demand appliances include:
- Electric vehicle chargers
- Heat pumps and electric furnaces
- Electric water heaters
- Induction cooktops and ovens
- Hot tubs and saunas
- Large air conditioners
Most homes never use all appliances at full power simultaneously, but panel sizing must assume a realistic worst‑case scenario. Electricians use detailed load calculations based on the Ontario Electrical Safety Code (OESC). This tool simply illustrates the relationship between kW and amperage.
Why Panel Upgrades Are Becoming More Common
Ontario homes are adding more electrical loads than ever before. Common reasons for panel upgrades include:
- Installing an EV charger
- Switching from gas to electric heating
- Adding a heat pump
- Finishing a basement or adding a rental suite
- Installing a hot tub or pool equipment
- Replacing older panels with limited breaker space
Even if your current panel technically supports your load, a larger panel may provide more flexibility for future upgrades.
Signs Your Panel May Be Undersized
Only a licensed electrician can diagnose electrical issues, but common signs of a stressed system include:
- Frequent breaker trips
- Limited space for new circuits
- Warm breakers or panel cover
- Lights dimming when large appliances start
- Use of multiple tandem breakers
If you notice any of these, an electrician can evaluate whether a panel upgrade is appropriate.
How Electricians Size Panels
Electricians use a formal load calculation that considers:
- Square footage of the home
- Number and type of major appliances
- Heating and cooling systems
- Electric vehicle charging
- Future expansion plans
This estimator is a simplified version that helps homeowners understand the basic math behind panel sizing.