Design tools · Panels

Panel-Size Helper

Thinking about an EV charger, a heat pump or solar? Tell us roughly what you have and what you’re planning, and we’ll give you a friendly first look at whether your panel is likely to keep up. It’s an estimate, and we’re happy to check it properly with you.

Check my panel Call (530) 401-7419, 24/7

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Check your panel

1. Your home today

Not sure? The main breaker, usually at the top of the panel, is stamped with the amps.

If you know the amps from the outdoor unit’s label, enter them and we’ll use that instead of the size.

2. What you’re planning
3. Assumptions (change these to match your labels)

When you don’t know a label rating, we use the values from the electrical code’s own worked example, or a plain placeholder. Your real numbers will be different, so use your labels if you have them.

The 12 kW range, 5 kW dryer, 4.5 kW water heater and 1.2 kW dishwasher are the values in the code’s worked example (Annex D). AC amps per ton is scaled from that same example (a 2½-ton heat pump at 24 amps); real units vary a lot, so the label is better. Some heat pump water heaters have a backup heating element and some run on 120 volts, so check the label. The hot tub, solar and battery numbers are placeholders. Solar and battery output only matter for the 120% check, not the load.

How we figured this

      Prefer the full contact form? Open it with this filled in.

      Estimate only. This is a rough, friendly first look, not a load calculation. It uses typical values where you don’t know your equipment’s ratings, and it can’t see your panel, wiring or meter. A licensed electrician has to do a real load calculation from your equipment labels before any panel, EV charger, solar or battery work, and the permit office reviews it.

      Want every line, both code methods, or a contractor-level check? Try the detailed Load Calculator.

      How the helper works

      1. 1
        The general load

        We follow the optional method the electrical code allows for a single-family home (NEC 220.82, used in California’s electrical code too). It adds up 3 volt-amperes (VA) for every square foot of living space, 1,500 VA for each kitchen and laundry circuit (at least two kitchen circuits and one laundry), and the label rating of appliances that are fastened in place or on their own circuit: range, dryer, water heater, dishwasher, EV charger, hot tub and so on (Lake County worksheet).

      2. 2
        Not everything runs at once

        The first 10,000 VA of that total counts in full. Everything above 10,000 VA counts at 40 percent, because a home rarely runs every appliance at the same time.

      3. 3
        Heating or cooling, whichever is bigger

        Then it adds only the largest of the heating and cooling choices: air conditioning at 100 percent; a heat pump at 100 percent, plus 65 percent of any backup strip heat; or electric furnace or baseboard heat at 65 percent (40 percent when there are four or more separately controlled units, which the helper doesn’t try to model). Heating and cooling aren’t added together.

      4. 4
        Turn it into amps

        The total in VA, divided by 240 volts, is the calculated load in amps. We compare that with your service size: at or under 80 percent of it we say “likely fits,” from 80 to 100 percent “tight,” and over 100 percent “likely needs an upgrade.” The 80 percent line is our own cautious rule of thumb, not a code rule.

      5. 5
        Solar and batteries, checked separately

        Solar and batteries don’t add to this load. They feed power back in, so the question is whether the panel’s bus bar can take it. We run the “120% rule” check below.

      A worked example, checked by hand

      Here’s the example from a California county’s worksheet (Lake County, and the same one at JADE Learning): a 2,800 sq ft home with a 14 kW range, 3 kW water heater, 5 kW dryer, 1.5 kW dishwasher, 15 kW of central electric heat and a 29-amp air conditioner.

      2,800 sq ft × 3 VA8,400 VA
      2 kitchen circuits + 1 laundry × 1,500 VA4,500 VA
      Range, water heater, dryer, dishwasher23,500 VA
      General load36,400 VA
      First 10,000 VA at 100% + 26,400 VA at 40%10,000 + 10,560 = 20,560 VA
      Heat at 65% (9,750 VA) vs AC at 100% (6,960 VA)9,750 VA
      Total ÷ 240 V30,310 VA ÷ 240 = about 126 amps

      Enter those same numbers in the helper (Electric for range, dryer, water heater and heat; 15 kW heat; label amps 29; and the kW values under Assumptions) and it shows the same 126 amps.

      California notes, in plain English

      • Solar and the 120% ruleWhen solar or a battery feeds back through a breaker in your panel, the main breaker plus 125 percent of the solar or battery output can add up to no more than 120 percent of the bus bar rating, and the solar breaker has to sit at the opposite end of the bus from the main. Put simply: the most backfeed you can add is 1.2 times the bus rating minus the main breaker. A 200-amp bus with a 200-amp main leaves room for a 40-amp backfeed breaker (City of Lodi checklist, Permit Sonoma).
      • When the 120% rule doesn’t fitThere are other paths: a “sum of the breakers” method, a smaller main breaker backed by a load calculation, a connection on the supply side of the main (which the utility has to approve), or a control system that limits the backfeed. Each one depends on your equipment, so we look at it on site.
      • EV energy management instead of an upgradeCalifornia’s 2025 electrical code is based on the 2023 NEC, which lets an energy management system limit an EV charger (or other loads) so the house stays under a set limit. When the system meets the code’s requirements, the load calculation can use that managed limit instead of the charger’s full rating (NEC 625.42 notes, 220.70 and Article 750). A charger turned down to a lower, locked setting is another option. Either way, it can save a panel upgrade for many homes.
      • EV charging counts as continuousThe code treats EV charging as a continuous load, so the charger’s circuit is sized larger than its output. A 40-amp charger usually goes on a 50-amp circuit.

      A plain summary, not legal advice. Your city or county enforces the code edition in effect when the permit is filed, plus any local rules.

      How IES helps

      • A real load calculationWe read your equipment labels and your panel and do the math properly, so you know where you stand.
      • Upgrade only if it’s neededIf load management or a smaller charger setting does the job, we’ll tell you.
      • Panel change-outs, handled start to finishWhen a new panel is the right call, we take care of the permit, the inspection, and the PG&E disconnect and reconnect.
      • Free estimatesNo pressure. Call (530) 401-7419, answered 24/7, or send your results below.

      Learn more about our work on panel and service upgrades, EV chargers, solar, batteries and renewable energy.

      Common questions

      How does the helper estimate my load?

      It follows the optional method that the electrical code allows for a single-family home: 3 volt-amperes per square foot for lights and outlets, 1,500 for each kitchen and laundry circuit, and the label rating of fixed appliances. The first 10,000 counts fully and the rest at 40 percent. Then it adds the biggest of your heating or cooling loads, and divides by 240 volts to get amps.

      Is a 100-amp panel enough?

      Sometimes. A smaller home with gas for cooking, drying, water heating and heat often fits fine. Adding an EV charger, a heat pump or an induction range is where 100 amps often gets tight. The helper shows where your mix lands, and a real load calculation settles it.

      Do I have to upgrade my panel for an EV charger?

      Not always. A lower charger setting, or an energy management system that limits charging when the house is busy, can let a charger fit on many existing services. California’s electrical code allows the managed limit to be used in the load calculation when the system meets the code’s requirements.

      What is the 120% rule for solar?

      When solar or a battery feeds back into a panel through a breaker, the panel’s bus bar can carry a little more than its rating, but only so much. Under the common “120% rule,” the main breaker plus 125 percent of the solar or battery output can add up to no more than 120 percent of the bus bar rating, with the solar breaker at the far end from the main. On a 200-amp panel with a 200-amp main, that leaves room for a 40-amp backfeed breaker.

      Why does my result say “tight”?

      It means the estimate lands close to your service size (from 80 to 100 percent of it, our own rule of thumb, not a code rule). Many homes in that range do fine with careful planning or load management, but it’s worth a closer look before you add more.

      Is this a real load calculation?

      No. It uses typical values where you don’t know the label rating, and every home is different. A licensed electrician needs to do a real load calculation from your equipment labels, and the permit office reviews it. Our estimates are free.

      Send your results for a free estimate

      Free estimates, no pressure. Tell us a little about the job and we’ll get back to you. Or call (530) 401-7419, answered 24/7.

      Name, a short description, and a phone number or email, please. We only use them to reply to you.

      Use the full form

      Sources

      The load method and California notes checked against the sources above in November 2026. Sources are listed for reference only; we don’t sell or endorse any brand.

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