Panel Capacity Checker

How this calculator works

This tool implements the NEC 220.82 Optional Method — the National Electrical Code's standard approach for calculating dwelling unit electrical loads. It's the same method a licensed electrician would use to determine whether your panel can support an EV charger without exceeding safe limits.

The calculation works in three steps:

1. General load: 3 VA per square foot, plus three 1,500 VA circuits for small appliances and laundry, plus nameplate ratings for all 240V appliances (range, dryer, water heater, etc.)
2. Demand factor: The first 10,000 VA of general load counts at 100%; everything above 10,000 VA counts at only 40%. This reflects the statistical reality that not everything runs at full power simultaneously.
3. HVAC + EV: The largest of your heating or cooling load is added at 100% (no demand factor). Your EV charger is added at 125% of its nameplate amperage — because EV charging is a continuous load per NEC 625.41.

Understanding your result

The result compares your total calculated load to 80% of your panel's rated capacity. For a 200-amp panel, that's 160 amps. The 80% rule comes from the NEC requirement that continuous loads not exceed 80% of a circuit's ampere rating.

• Green (Safe): Your total load is below 90% of safe capacity — you have comfortable headroom.
• Amber (Warning): You're between 90–100% of safe capacity. The charger technically fits, but there's little margin. Consider a smart load-managing charger.
• Red (Exceeds): Your calculated load exceeds safe panel capacity. A panel upgrade, a lower-amperage charger, or load management is needed.

Common scenarios: will my panel fit an EV charger?

The answer depends heavily on your home's existing load. Here are typical outcomes for common configurations:

• 200A panel, gas heat, no electric range: Almost always has room for a 40–48A charger. This is the most favorable scenario.
• 200A panel, heat pump, electric range + dryer: Tight. A 32A charger often fits; 40A may show a warning. Smart load management is worth considering.
• 100A panel, any configuration: Usually needs an upgrade for a Level 2 charger beyond 16–24A. A 100A panel has only 80A of safe continuous capacity — not much room once HVAC and appliances are accounted for.
• 100A panel, gas heat only, minimal appliances: A 24–32A charger may be feasible. Run the calculator with your exact loads to confirm.

Smart load management: an alternative to panel upgrades

If your panel is at or near capacity, a smart load-management charger can automatically reduce charging speed when your home's other loads are high — preventing the panel from being overloaded. Brands like ChargePoint, Emporia, and Wallbox offer chargers with built-in load management.

This is often far cheaper than a full panel upgrade ($200–500 for a smart charger vs. $2,000–5,000 for a panel upgrade), though it does mean your EV charges more slowly on evenings when your HVAC, oven, and dryer are all running simultaneously.

What to expect from the electrician visit

Once you've checked your panel capacity here, the next step is a licensed electrician. Here's what typically happens during an EV charger installation consultation:

1. Panel inspection: The electrician opens your panel and reads the actual nameplate ratings of your equipment — not the assumed values used in planning tools like this one.
2. Slot availability check: Even if your panel has amperage headroom, it needs an open circuit slot for the new 40–60A breaker. Tandem breakers can create a slot if none are available, but not all panels support them.
3. Wire run assessment: The cost of running wire from your panel to the garage (or wherever the charger will be installed) is often a major portion of the total project cost. Long runs through finished walls can add $500–1,500 to the job.
4. Permit and inspection: EV charger installations require a permit in most US jurisdictions. The permit fee is typically $50–150, and an inspector will verify the work after completion. Never skip the permit — it protects you at resale and in case of an insurance claim.

When to consult a professional

This tool gives you an accurate planning estimate, but it uses standard nameplate assumptions. Before any electrical installation, have a licensed electrician:

• Read the actual nameplate VA of your specific appliances
• Inspect your panel for available breaker slots and bus bar capacity
• Pull the required permit for the EV charger installation
• Confirm the calculation under your local jurisdiction's adopted code edition

Most electricians complete a panel capacity assessment during the EV charger consultation visit (typically $75–$150 for a one-hour assessment). If your panel needs an upgrade, get 2–3 quotes — prices vary significantly by region and contractor.