Electrical Load Calculator
This free electrical load calculator runs a real NEC Article 220 dwelling calculation instead of the “1 amp per 100 square feet” rules of thumb that either oversize your panel or leave you short. It applies the actual demand factors the code uses — the 3 VA/ft² general-lighting load reduced by Table 220.45, the 8,000 VA credit a 12 kW range gets under Table 220.55, the dryer and fixed-appliance factors — then divides by 240 V and rounds up to a standard service size.
Two methods are built in. The Standard method (Part III) applies each demand table separately and is the traditional long-form calculation. The Optional method (220.82) is the simpler whole-house approach most modern services use: 100% of the first 10 kVA of general load plus 40% of the rest, then the single largest heating-or-cooling figure. There is also an existing-dwelling mode (220.83) to check whether your current panel can absorb a new A/C, heat pump, or EV charger.
It sizes the service or feeder only — not individual branch circuits — and it is a screening estimate, not a stamped design: the adopted NEC edition and local amendments vary, and a permitted job needs a licensed electrician and your AHJ. For the circuit side of a specific load, pair it with the wire-size and breaker-size calculators. Free, no signup.
Electrical Load Calculator
Size a dwelling's electrical service with an NEC Article 220 load calculation — Standard or Optional method — and get the minimum service amps and conductor. Free, no signup.
Method & code
The Standard method applies each demand table separately; the Optional method (220.82) is the simpler whole-house calc most homes use.
The dwelling
General lighting and receptacles are 3 VA/ft² (2 VA/ft² under the 2026 NEC), from outside dimensions.
Minimum two 20 A small-appliance circuits + one laundry circuit, each 1,500 VA (220.52).
Major appliances
Enter nameplate kW. Leave a field at 0 or blank if you don't have it.
Optional method: range, dryer, and all appliances count at nameplate (dryer minimum 5 kW).
Heating & cooling
Heat and A/C are noncoincident — only the larger counts (220.60).
Optional method (220.82(C)): fewer than 4 separately-controlled heat units = 65%; 4 or more = 40%.
Calculation Formulas
Dwelling general lighting and all 20 A general-use receptacles are covered by a 3 VA/ft² unit load (2 VA/ft² under the 2026 NEC), calculated from outside dimensions and excluding open porches and unfinished spaces not adaptable for future use.
Example:
2,000 ft² × 3 VA/ft² = 6,000 VA of general lighting/receptacle load.
A dwelling requires at least two 20 A small-appliance branch circuits and one laundry branch circuit, each counted at 1,500 VA (220.52).
Example:
Two small-appliance + one laundry = 3 × 1,500 = 4,500 VA.
The combined general-lighting + small-appliance + laundry total is reduced by the dwelling demand factors, because not all lighting and receptacle load runs at once.
Example:
9,000 VA subtotal → 3,000 + (6,000 × 0.35) = 5,100 VA net.
Household cooking appliances get a large diversity/demand credit — a single 12 kW range is calculated at only 8 kW. Ranges over 12 kW increase Column C by 5% for each kW (or major fraction) above 12 (Note 1).
Example:
One 12 kW range = 8,000 VA; one 15 kW range = 8,000 × 1.15 = 9,200 VA.
Each household dryer is calculated at 5,000 VA or its nameplate, whichever is larger. A single dwelling dryer takes 100%.
Example:
A 5.5 kW dryer = 5,500 VA (nameplate > 5 kW floor).
Four or more fastened-in-place appliances (other than range, dryer, space heat, and A/C) on the same service get a 75% demand factor; fewer than four count at 100%.
Example:
Water heater 4,500 + dishwasher 1,200 + disposal 900 + microwave 1,500 = 8,100 → ×0.75 = 6,075 VA.
Space heating and cooling are noncoincident — they never run together — so only the larger load is added to the service calculation.
Example:
9,000 VA heat vs 5,760 VA A/C → include 9,000, drop the A/C.
The service calculation adds 25% of the largest motor load (the code requires the largest motor at 125% of its rating).
Example:
Largest motor 1,200 VA → +300 VA to the service total.
For a dwelling on a single 120/240 V service ≥ 100 A, sum all general loads at nameplate, apply the 10 kVA/40% factor, then add the single largest 220.82(C) heating/cooling value (A/C 100%, ≥4 heat units 40%, <4 units 65%). The 2026 NEC drops the first tier to 8 kVA.
Example:
29,700 VA general → 10,000 + (19,700 × 0.40) = 17,880; + 3,600 VA heat = 21,480 VA.
The calculated VA is divided by 240 V, rounded up to the next standard overcurrent device, and floored at the 100 A one-family minimum. The service conductor is then read from Table 310.12 (the dwelling 83% allowance).
Example:
21,480 VA ÷ 240 = 89.5 A → 100 A service → 4 AWG Cu / 2 AWG Al.
Standard Constants
| Constant | Value | Description |
|---|---|---|
| General lighting unit load | 3 VA/ft² (2 VA/ft² in 2026 NEC) | Dwelling general lighting + general-use receptacles (220.41 / 220.12). |
| Small-appliance / laundry circuit | 1,500 VA each | Per 220.52(A) and 220.52(B). |
| Lighting demand brackets | 100% / 35% / 25% | First 3 kVA, 3–120 kVA, and remainder (Table 220.45 / 220.42). |
| One range ≤ 12 kW | 8,000 VA | Table 220.55 Column C, single appliance. |
| Dryer minimum | 5,000 VA | Or nameplate if larger (220.54). |
| Fixed-appliance demand | 75% at 4+ appliances | Fastened-in-place appliances (220.53). |
| Largest-motor adder | 25% | Added to the service/feeder calc (220.50 / 430.24). |
| Optional first tier | 100% of 10 kVA | Then 40% of the remainder (220.82(B); 8 kVA in 2026). |
| One-family service minimum | 100 A | Service disconnect rating floor (230.79(C)). |
| Dwelling conductor allowance | 83% of service rating | Table 310.12 for 120/240 V 3-wire dwelling services. |
Note: All calculations include appropriate waste factors based on project complexity and material type. Results are estimates and should be verified by professionals before purchasing materials.
NEC Article 220 — Branch-Circuit, Feeder, and Service Load Calculations(NFPA 70, Art. 220)
View StandardThe core methods for calculating dwelling service and feeder load: the Standard method (Part III) and the Optional method (220.82).
Key Requirements:
- •General lighting 3 VA/ft² (220.41 in 2023, 220.12 in 2020; 2 VA/ft² in 2026)
- •Table 220.45 / 220.42 lighting demand factors (100% / 35% / 25%)
- •Table 220.55 range and Table 220.54 dryer demand factors
- •220.60 noncoincident heat-vs-A/C rule; 220.53 fixed-appliance 75%
- •220.82 optional method (100% of first 10 kVA + 40% remainder)
NEC 230.79 — Rating of Service Disconnecting Means(NFPA 70, 230.79(C))
View StandardSets the minimum service disconnect rating for a one-family dwelling.
Key Requirements:
- •One-family dwelling service disconnect not less than 100 A, 3-wire
- •Applies even when the calculated load is below 100 A
NEC 240.6 — Standard Ampere Ratings(NFPA 70, 240.6(A))
View StandardThe standard overcurrent-device ratings the calculated load rounds up to.
Key Requirements:
- •Standard sizes 100, 110, 125, 150, 175, 200, 225 A and up
- •“320 A” is not a standard rating — a 400 A-class meter uses a 400 A device
NEC Table 310.12 — Dwelling Services & Feeders (83% rule)(NFPA 70, 310.12)
View StandardReduced conductor sizes permitted for a 120/240 V 3-wire dwelling service/feeder carrying the entire load.
Key Requirements:
- •Conductors may be rated 83% of the service rating
- •100 A = 4 AWG Cu / 2 AWG Al; 200 A = 2/0 AWG Cu / 4/0 AWG Al
- •Valid only with no ampacity adjustment/correction factors; otherwise use Table 310.16
NEC 220.83 — Existing Dwelling Unit(NFPA 70, 220.83)
View StandardChecks whether an existing service or feeder can carry additional load.
Key Requirements:
- •First 8 kVA at 100% + remainder at 40%
- •New A/C or electric heat is added at 100% (220.83(B))
- •It is an adequacy check, not a new-service sizing method
Standards Disclaimer: Standards and codes are subject to periodic updates. Always verify current requirements with local building authorities and professional engineers before beginning construction. Links provided are for reference only.
Adopted NEC edition
Jurisdictions run different code years
States adopt the NEC on their own schedule — 2017, 2020, 2023, and increasingly 2026 are all in force somewhere. The demand values are stable across 2020/2023, but 2026 (renumbered to Article 120) drops general lighting to 2 VA/ft² and the optional first tier to 8 kVA.
Regional Examples:
Garage & unfinished area
What counts in the floor area
The 2020 NEC excludes attached garages and unfinished/unadaptable space from the floor area; the 2023 NEC includes attached garage area in the dwelling load. The 2026 edition re-excludes only detached garages.
Regional Examples:
EV charger treatment
Genuinely unsettled under 2020/2023
There is no consensus on whether EV supply equipment may ride the 40% optional tier or must be added at 100% (or 125% as a continuous load). The 2023 NEC added 220.57 (EVSE = 7,200 VA minimum); the 2026 NEC settles it at 100% with no demand factor.
Regional Examples:
Conductor ampacity adjustments
When the 83% table does not apply
Table 310.12 assumes a 120/240 V 3-wire dwelling service with no ampacity adjustment or correction factors. Conduit fill, high ambient temperature, or bundling can force sizing from Table 310.16 instead.
Regional Examples:
Local amendments
Cities and states modify the NEC
Some jurisdictions amend Article 220 or set their own minimum service (often 150 or 200 A for new construction). A calculated 100 A result may still be overruled by a local minimum.
Regional Examples:
Before You Build
- •Contact your local building department for specific requirements
- •Verify frost line depths, wind zones, and seismic requirements for your area
- •Check if permits are required and schedule required inspections
- •Consult with a local contractor familiar with local codes
Want to Learn More?
How to size a home electrical service with an NEC Article 220 load calculation — the Standard and Optional methods, demand factors, and reading the result.
Read the How to Do an Electrical Load Calculation (NEC 220)
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How to Use This Calculator
- Pick the calculation method (Optional 220.82 is simplest for a whole house) and your adopted NEC edition.
- Enter the dwelling floor area and the number of small-appliance and laundry circuits.
- Add your major appliances by nameplate kW — range, dryer, water heater, and other fixed appliances.
- Enter electric heat and air conditioning; only the larger of the two counts (noncoincident, 220.60).
- Click Calculate for the total VA, the minimum service amps, and the service conductor (copper and aluminum).
Standard vs Optional method — which to use
Both methods are code-legal and usually land within a service size of each other. The Standard method (Article 220 Part III) applies each demand factor separately — lighting via Table 220.45, cooking via Table 220.55, the dryer via Table 220.54, four-or-more fixed appliances at 75%, and 25% of the largest motor — and is what you will see in a formal load-calc worksheet. The Optional method (220.82) is a shortcut allowed for a dwelling on a single 120/240 V service of 100 A or more: total every general load at nameplate, take 100% of the first 10 kVA and 40% of the remainder, then add the largest single heating-or-cooling selection. It is faster and usually the one contractors run for a straightforward house. Whichever you use, the result is divided by 240 V, rounded up to the next standard breaker size in 240.6(A), and floored at the 100 A one-family minimum (230.79(C)); the conductor then comes from Table 310.12, the dwelling “83%” allowance. This tool sizes the service, not branch circuits — verify the final design with a licensed electrician and your local inspector.
Frequently Asked Questions
What size electrical service do I need for my house?
It depends on your square footage and appliances, not a flat rule of thumb. Run an NEC Article 220 load calculation: a typical 2,000 sq ft home with an electric range, dryer, water heater, and central air commonly lands between 100 and 200 A. This calculator does the real math both ways — the Standard method and the Optional method (220.82) — and rounds up to the next standard service size, with the 100 A one-family minimum (230.79(C)) always enforced.
What's the difference between the Standard and Optional methods?
Both are code-legal and usually agree within one service size. The Standard method (Article 220 Part III) applies each demand factor separately — lighting via Table 220.45, cooking via Table 220.55, dryer via Table 220.54, four-or-more fixed appliances at 75%, plus 25% of the largest motor. The Optional method (220.82) is the shortcut most contractors use for a whole house: total all general loads at nameplate, take 100% of the first 10 kVA and 40% of the rest, then add the single largest heating-or-cooling figure.
Why does a 12 kW range only count as 8,000 VA?
Because of the diversity credit in NEC Table 220.55. You never run every burner and the oven at full power simultaneously for long, so the code lets a single household range of 12 kW or less be calculated at just 8 kW (8,000 VA). Ranges over 12 kW add 5% to that figure for each kW above 12 (Note 1), so a 15 kW range calculates at 9,200 VA. It's one of the biggest reasons a rule-of-thumb estimate oversizes a panel.
Does my air conditioner or my heat count in the load?
Only the larger of the two. Heating and cooling are 'noncoincident' loads under NEC 220.60 — they never run at the same time — so the calculation includes whichever is bigger and drops the smaller entirely. If your electric heat is 9,000 VA and your A/C is 5,760 VA, the heat is counted and the A/C is omitted. Enter both and the calculator picks the larger automatically.
Can I add an EV charger or A/C to my existing panel?
Use the existing-dwelling mode (NEC 220.83). It checks whether your current service can absorb a new load: it takes 100% of the first 8 kVA of existing load plus 40% of the remainder, and adds new A/C or electric heat at 100%. If the total exceeds your existing service rating, you need a service upgrade. Note that EV-charger treatment is genuinely unsettled under the 2020/2023 NEC — confirm with your AHJ.
What wire size do I need for the service?
For a standard 120/240 V, 3-wire dwelling service carrying the whole load, NEC Table 310.12 lets the conductors be sized at 83% of the service rating — so a 200 A service uses 2/0 AWG copper or 4/0 AWG aluminum, and a 100 A service uses 4 AWG copper or 2 AWG aluminum. This calculator shows both. That allowance only applies with no ampacity adjustment or correction factors; hot attics, conduit fill, or long runs push you to Table 310.16 instead.
Is this calculator a substitute for an electrician?
No. It's a screening and planning tool that sizes the service or feeder — not individual branch circuits — and it can't see everything a permitted design must account for. Adopted NEC editions and local amendments vary by jurisdiction, and many areas set their own minimum service for new construction. Use it to right-size before you shop and to sanity-check a proposal, then have a licensed electrician confirm the final design with your AHJ.