Choose Residential or Commercial, select the voltage system, enter the load details, and click Calculate. Both modes work standalone or together with the phase/leg balance section below.
Percent of rated capacity used by your required load (with spare-space headroom) across neighboring standard load-center sizes. Your recommended size is highlighted in gold; the dashed line marks 100% capacity.
Add individual circuits below and assign each to a leg or phase — this works together with the mode above using the same voltage system selection. Runs automatically as part of Calculate.
Add circuits above, then click Calculate, to see leg/phase balance.
Results are engineering estimates based on published NEC Article 220 formulas and demand-factor tables (220.12, 220.42, 220.52, 220.53, 220.54, 220.55, 220.56, 220.60, 220.14(I)) and NEC 430.24. Several simplifications are disclosed in the Comprehensive Guide below. Actual sizing varies with installation conditions and the adopted NEC edition. Verify with a licensed electrician before any electrical work.
Common standard load-center/panel ratings and typical use case, for orientation — not a substitute for the calculated result above.
| Standard Size | Typical Use |
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Four real-world scenarios. Click "Load This Example" to run it in the calculator above.
The NEC 220 Part III standard method (Residential)
General lighting load is calculated at 3 VA per square foot (NEC Table 220.12), plus at least two 1,500 VA small-appliance circuits (NEC 220.52(A)) and at least one 1,500 VA laundry circuit (NEC 220.52(B)). That subtotal is demand-factored per NEC Table 220.42: the first 3,000 VA at 100%, the next up to 120,000 VA at 35%, and any remainder at 25% — reflecting that a dwelling rarely runs every circuit simultaneously at full load.
Fixed appliances and the 75% rule
NEC 220.53 permits a 75% demand factor when four or more fixed appliances (other than range, dryer, space-conditioning equipment, or laundry) are on the same feeder or service. Fewer than four appliances are counted at 100%. This calculator applies that threshold automatically based on how many appliances you've added to the list.
Range and dryer sizing (single-appliance case)
NEC Table 220.55, Column C, sets an 8 kW demand for a single range rated up to 12 kW, increasing 5% per kW (or major fraction) above 12 kW, up to 27 kW. NEC 220.54 sets dryer demand at 100% of nameplate rating, with a 5 kW minimum for a single dryer. Multiple ranges or dryers on one service use different table columns and are not modeled here.
HVAC and noncoincident loads
NEC 220.60 permits counting only the larger of heating or cooling load when the two are noncoincident — a home or building rarely runs full heating and full cooling at the same time. This calculator takes the larger of your entered heating/cooling values and applies a 125% continuous-duty factor (NEC 210.20(A)), since HVAC equipment commonly runs three hours or more continuously.
The largest-motor 25% adder
NEC 430.24 requires feeder conductors supplying multiple motors to be sized for the sum of all motor full-load currents, plus 25% of the largest motor's full-load current — because the largest motor's starting (inrush) current adds meaningfully to peak demand even though it's brief. Enter your largest single motor's connected VA and this calculator adds that 25% on top of the total demand.
Commercial occupancy-based method
Commercial mode starts from NEC Table 220.12's published VA/ft² figures by occupancy type, applied at 100% of connected value — a deliberately conservative simplification rather than modeling every occupancy-specific demand-factor row of NEC Table 220.42, consistent with how several comparable commercial load tools in the market handle this. General-use receptacles not already covered by a unit lighting load are added at 180 VA each per NEC 220.14(I).
Kitchen equipment demand (restaurant occupancy)
NEC Table 220.56 permits a demand factor based on the number of pieces of kitchen equipment on a feeder: 100% for two or fewer units, stepping down to 65% for six or more. This calculator applies that published step table to your entered kitchen equipment count and total connected kVA when Restaurant occupancy is selected.
Spare space / future-expansion allowance
Since the load for an anticipated future circuit is undetermined at design time, a common planning practice is to add roughly 10A of headroom per reserved breaker space before selecting a standard load-center size. This calculator lets you set that count directly (default 2) and adds the headroom before rounding up.
Phase / leg balance (working together with either mode)
On a 120/240V split-phase service, loads should be distributed as evenly as practical between L1 and L2; on a three-phase service, across A, B, and C. Meaningful imbalance increases neutral conductor current and can strand usable capacity on the lighter leg or phase. This calculator's balance section reads whichever mode (Residential or Commercial) and voltage system is active, letting you add individual circuits and see the resulting distribution — a planning-level estimate, not a certified neutral-conductor calculation.