Commercial Load Calculator
Feeder and service load for a commercial (non-dwelling) building by the NEC Article 220 Part III standard method. Pick the occupancy, enter the floor area, receptacle count, and any show-window, sign, or kitchen loads; get the calculated load, the 125% continuous minimum ampacity, and a standard service size, with every demand-factor step shown so it can be checked line by line.
How to use this calculator
- Select the occupancy type. This sets the general-lighting unit load from NEC Table 220.12 (office and bank 3.5 VA/ft², store 3, restaurant 2, warehouse 0.25, and so on).
- Enter the floor area from outside dimensions and the number of general-use receptacle outlets. Each single or multiple receptacle on one strap counts as 180 VA (220.14(I)).
- Add the optional loads that apply: show-window lighting (200 VA per linear foot), a 1,200 VA sign circuit, and commercial kitchen equipment (unit count plus total nameplate VA for the Table 220.56 demand factor).
- Pick the service voltage and phase. Read the calculated load, the minimum ampacity with the 125% continuous factor, and the recommended standard service size.
NEC reference
This calculator implements NEC 2017 Article 220 Part III (standard calculation method, non-dwelling): general lighting from Table 220.12 with the Table 220.42 demand factors (100% for most occupancies; warehouse, hospital, and hotel tiers where they apply); receptacle outlets at 180 VA each per 220.14(I) with the Table 220.44 demand factor; show-window lighting per 220.43; sign circuits per 220.14(F); and commercial kitchen equipment per Table 220.56. Continuous loads take the 125% multiplier for feeder and service sizing (215.3, 230.42), and the service rating follows the standard ampere ratings of 240.6(A). Note that the 2020 NEC rebuilt Table 220.12 with ASHRAE-based values and renumbered the lighting demand table to 220.42. This v1 uses the 2017 classic values, so confirm your adopted edition. Motor loads, HVAC selection, and the dwelling methods are handled by separate tools.
Results are for reference only. Verify against the applicable adopted edition of the NEC and consult a licensed electrician for code compliance.
Worked example: 5,000 ft² office
| Line | VA |
|---|---|
| General lighting: 5,000 ft² × 3.5 VA (Table 220.12, office) | 17,500 |
| Lighting demand factor (Table 220.42, all others @ 100%) | 17,500 |
| Receptacles: 40 outlets × 180 VA (220.14(I)) | 7,200 |
| Receptacle demand (Table 220.44, ≤ 10 kVA @ 100%) | 7,200 |
| Calculated load (Article 220) | 24,700 |
| Minimum ampacity basis: 1.25 × 17,500 (lighting, continuous) + 7,200 | 29,075 |
On a 208Y/120 V three-phase service, 24,700 VA ÷ (208 × √3) = 68.6 A calculated load; the 29,075 VA minimum-ampacity basis ÷ (208 × √3) = 80.7 A, which rounds up to a 90 A standard service. These are the same numbers the calculator returns for its default inputs, so you can check the tool against the worked example directly.
Frequently asked questions
Why is the general-lighting number the minimum, not the actual fixtures?
Table 220.12 sets a minimum general-lighting load per square foot regardless of the installed fixture count, so the service can absorb future lighting changes. If the actual connected lighting is larger, you size to the larger figure. For office and bank buildings the code historically allowed using actual connected load where it is lower, but the table value is the safe default this calculator uses.
Which NEC edition are these unit loads?
The 2017 (and identical 2014/2011) Table 220.12 classic values. The 2020 NEC reconstructed the table using ASHRAE 90.1 and IECC lighting-power densities. The office value dropped from 3.5 to about 1.3 VA/ft², and those numbers already include the 1.25 continuous factor. Many jurisdictions are still on the 2017 code; confirm which edition your AHJ enforces before relying on a unit load.
Do I apply demand factors to receptacles or to lighting?
Both, with different tables. General lighting uses Table 220.42 (100% for most occupancies; reduced tiers for warehouses, hospitals, and hotels). Non-dwelling receptacle loads calculated at 180 VA per outlet use Table 220.44: the first 10 kVA at 100% and the remainder at 50%. This tool applies each automatically and shows the before-and-after figures.
What is left out of this calculation?
Motor loads and the 25% largest-motor addition (220.50, 430.24), noncoincident heating versus air-conditioning selection (220.60), multi-outlet assemblies (220.14(H)), and the dwelling methods. Enter a known motor or HVAC figure in the "other loads" field if you have already demand-adjusted it, and use the dedicated motor and wire-sizing tools for those parts.
Related calculators
- Electrical Load Calculator: the dwelling (residential) service load per NEC 220.82.
- Wire Size Calculator: size the feeder and service conductors for the calculated load.
- Breaker Size Calculator: the overcurrent device for the branch circuits and feeders.
- Voltage Drop Calculator: check the feeder run for long distribution circuits.
Studying for the licensing exam? Our own NEC Code Quickstart works all twelve exam calculations start to finish, each with the code reference. Also in paperback.
Running an electrical contracting business? Jobber handles scheduling, invoicing, and job management. Start a 14-day free trial.
For deeper NEC training on commercial load calculation and service sizing, Mike Holt's NEC courses are the industry standard.
Working from the printed code? NEC code books and tab sets are available from Mike Holt.
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