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Home Electrical Service Panel Amperage Sizing Calculator

Estimate the minimum electrical service amperage needed for a dwelling, using a simplified NEC 220 general load calculation.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax

Estimated required service amperage

27.11 A

Low confidence

This is a SIMPLIFIED illustrative version of the NEC 220 standard method, omitting several real-world factors (HVAC load, EV chargers, largest motor load addition, optional calculation method). It is NOT a substitute for a complete NEC Article 220 load calculation performed by a licensed electrician, which determines your actual required service size and is required for permitting. Always round up to the next standard breaker/service size (100A, 125A, 150A, 200A) and consult your electrician.

Total connected load (before demand factor)
13020.84 VA
Demand load (after NEC 220.42 factor)
6507.29 VA

With the figures above, the estimated required service amperage comes to 27.1. Note that service voltage (v, commonly 240 for us dwellings) sits at the high end of the range this calculator was checked against, so treat the output as indicative rather than settled. Treat this one cautiously — the confidence rating is low, so verify it against a merchant quote or a trade opinion first. This is calculated for United States and cites IRC 2024. Building in another market? Change the selector above so the units and code reference follow.

Add the equipment this sizes

This result is a specification — 27.114 A — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • Simplified NEC Article 220 standard method: general lighting load = floor area × 3 VA/ft² (NEC 220.12); total connected VA = general lighting + small appliance circuits (1500 VA each) + laundry circuit (1500 VA) + fixed appliance nameplate VA; a demand factor is then applied per NEC Table 220.42 (100% of the first 3000 VA, 35% of the remainder); required amperage = demand VA ÷ voltage

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Frequently asked questions

How is the required service amperage calculated here?
General lighting load is estimated at 3 VA per square foot of dwelling floor area (NEC 220.12), then added to the small-appliance circuits (1500 VA each), laundry circuit(s) (1500 VA each), and fixed appliance nameplate load. A demand factor per NEC Table 220.42 (100% of the first 3000 VA, 35% of the remainder) is applied to the total, and the resulting demand VA is divided by the service voltage to get amps.
Why is a demand factor applied instead of just adding up every load?
Not every circuit in a home draws its full rated load at the same time, so NEC Table 220.42 allows the connected load above the first 3000 VA to be counted at only 35% for sizing purposes — this reflects realistic diversity in how a dwelling's loads actually operate together.
Is this result enough to size and permit my actual service panel?
No. This is a simplified illustrative version of the NEC 220 standard method that omits real-world factors such as HVAC load, EV chargers, and the largest-motor load addition. It is not a substitute for a complete NEC Article 220 load calculation performed by a licensed electrician, which is required for permitting — always round up to the next standard breaker/service size (100A, 125A, 150A, 200A) and consult your electrician.