Load Calculator

For a building with any number of units you add up the lights and outlets for all the units (3 VA per square foot plus 1,500 VA for each small-appliance and laundry circuit), then count the first 3,000 VA fully, the next 117,000 VA at 35% and the rest at 25%. Ranges use Column C of the cooking table for the whole count, dryers use the dryer table, four or more fastened-in-place appliances count at 75%, and heating or cooling counts at the larger of the two. Our panel follows the published Annex D example. When the units have electric cooking or heat, the 220.84 optional method is often lower, so it’s worth trying both.

In buildings like these, not every light is on at once, so the code lets the general lighting load on a feeder or service count in steps (Table 220.45). Hotels: 60% of the first 20,000 VA, 50% of the next 80,000, 35% of the rest. Hospitals: 40% of the first 50,000 VA, 20% of the rest. Warehouses: the first 12,500 VA fully and half the rest. The steps aren’t used for areas where all the lights are likely on together, like operating rooms or ballrooms.

It suggests which phase or leg each load goes on so no phase is much heavier than the others. It places the biggest loads first, each on the phase that has the least so far. It’s a starting layout: real panels also depend on open breaker spaces and on which loads run together.

The code has a few busbar options, and only one has to work: the 100% rule, the 120% rule with the solar breaker at the far end from the main, a center-fed version of the 120% rule for homes, and the sum rule, where every breaker on the bus except the main adds up to no more than the bus rating. If none fits, the usual fixes are a smaller main breaker (if the load calculation allows), a bigger panel, a power control system, or a connection on the supply side of the main. Your inspector and the panel label have the final say.

The code’s notes recommend about 3% on a branch circuit and 5% for the feeder and branch circuit together. It’s a recommendation, not a rule, but long runs to a shop, well pump or EV charger can lose enough voltage to matter. The calculator suggests the smallest wire that meets your target. That only covers voltage drop; the wire still has to be big enough for the breaker.

Chapter 9 of the code allows 53% of the conduit’s inside area for one wire, 31% for two and 40% for three or more, using the listed area of each wire and conduit. Count the ground wire too. Long runs with many bends may need more room so the wires pull without damage.

Only the section numbers. In the 2026 NEC the load calculation article moved from Article 220 to Article 120 (220.82 becomes 120.82, for example) and energy management moved from Article 750 to Article 130. The math still follows the 2023 NEC, which California’s current code is based on. The 2026 edition also changes some values, which we haven’t applied.

The standard method (Article 220, Part III) applies a separate demand rule to each kind of load: lights and outlets, fixed appliances, the dryer, cooking, heating or cooling, and motors. The optional method (220.82) adds almost everything at its label rating, counts the first 10,000 VA fully and the rest at 40 percent, then adds the largest heating or cooling choice. For a typical one-family home the optional method often comes out lower. You use one method, not a mix.

When you’re adding loads to a home whose service is already there, such as a remodel, an EV charger or a new heat pump, and want to see if the existing service can carry it. It counts the first 8,000 VA fully and the rest at 40 percent. If new air conditioning or electric heat is part of the job, the larger of those is added at 100 percent on top.

Ranges rarely run every element at once, so the code’s cooking table gives one household range up to 12 kW a demand of 8 kW in the standard method. Bigger ranges go up 5 percent for each kilowatt (or major fraction) over 12. Smaller cooktops and wall ovens use a percentage of their label rating instead.

In the 2023 NEC, which California’s 2025 code is based on, an EV charger counts at its label rating or 7,200 VA, whichever is larger, in the standard method. An energy management system that meets the code can let the calculation use a lower managed limit, which can save a service upgrade.

Yes, for a first look. Under More calculations there are panels for multifamily buildings (the 220.84 optional method, three or more units), commercial spaces (lighting by occupancy, receptacles, kitchen equipment and other loads), and existing services sized from measured demand (220.87). They are estimates; a commercial or multifamily job needs a licensed electrician or engineer to prepare the real calculation.

No. It’s an estimate to help you plan. A licensed electrician has to prepare the real calculation from your equipment labels, and your city or county may have local amendments or its own worksheet. Our estimates are free.