What a dwelling load calculation actually answers
A dwelling load calculation answers one question: how many amperes must the service or feeder be able to carry? You never add up every nameplate in the house, because no house runs every appliance at once. Article 220 instead gives you a set of demand factors — legally defensible discounts — that turn a connected load of 60,000 VA into a calculated load of 35,000 VA. The calculated load is what the utility, the plan reviewer and the inspector all work from.
You need this number in four common situations. You are pulling a permit for new construction and must show a worksheet. You are upgrading a 100 A panel and need to prove the existing house fits, or that it does not. You are adding an EV charger, a heat pump or a hot tub and have to demonstrate the service still has room. Or you are studying for a journeyman or master exam, where Article 220 questions are guaranteed to appear.
The standard method on this page is the long-form calculation in Part III of Article 220. It is more work than the optional method of 220.82, and for an all-electric house it usually returns a larger number. That is not a defect. The standard method is the one that always applies; the optional method is a permission with conditions attached. When the two disagree, you may use either result that the code allows, and most designers run both and take the smaller.
Every line of the worksheet, and why it is there
General lighting and general-use receptacles: 3 VA per square foot. You measure the outside dimensions of the habitable space and exclude open porches, garages, and unfinished areas not adaptable for future use. The code does not care how many receptacles you install, because that count is unpredictable; it uses area as a proxy. A 2,000 ft² house therefore contributes 6,000 VA before any discount. In the 2023 NEC this rule sits in 220.41; older editions carry the same 3 VA/ft² figure in 220.12.
Small-appliance and laundry circuits: 1,500 VA each. 210.11(C)(1) requires at least two 20 A circuits for the kitchen and dining receptacles, and 210.11(C)(2) requires a laundry circuit. Each one is entered at 1,500 VA whether or not anything is plugged into it, because those circuits are reserved for loads the general lighting allowance does not cover.
The demand factor on that subtotal. Add the lighting, small-appliance and laundry figures together and apply Table 220.45: the first 3,000 VA counts at 100%, everything from 3,001 to 120,000 VA counts at 35%, and anything beyond that counts at 25%. The 35% band is doing nearly all the work in a house — it reflects the measured reality that lighting and receptacle loads are highly diversified.
Cooking appliances: Table 220.55. A single household range is not counted at nameplate. Ranges over 8¾ kW through 12 kW are counted at a flat 8 kW under Column C. Above 12 kW you add 5% to that 8 kW for each additional kilowatt or major fraction. Below 8¾ kW you use a percentage from Column A or Column B instead, and for a single appliance both columns read 80%: an 8 kW cooktop counts 8,000 × 0.80 = 6,400 VA. The two columns only diverge once you have two or more cooking appliances, where Column A drops to 75% and Column B to 65%. This calculator covers one cooking appliance; for two or more, or for ranges of unequal rating, work Notes 1 through 3 of Table 220.55 by hand.
Clothes dryer: 220.54. A dryer is counted at nameplate or 5,000 VA, whichever is larger. A 4.5 kW dryer still contributes 5,000 VA. Demand factors apply only when there are five or more dryers, so a house always counts one at 100%.
Fastened-in-place appliances: 220.53. Water heater, dishwasher, disposal, built-in microwave, attic fan and similar equipment are added at nameplate — and if there are four or more of them, you may take 75% of the total. Ranges, dryers, space heating and air conditioning are deliberately excluded here because they already have their own rules.
Heating versus cooling: 220.60. Two loads that cannot physically run at the same time are noncoincident, and you count only the larger. A gas-heated house with a 5 kVA condenser counts 5,000 VA; an all-electric house with 10 kW of strip heat and the same condenser counts 10,000 VA. A heat pump is the exception worth watching: if the controls allow the compressor and the auxiliary strip heat to run together — and on many systems they do, in defrost or in deep cold — you must count both.
The largest motor: 220.50 and 430.24. Motor loads are computed at 125% of the largest motor, which in practice means adding a 25% adder for one motor somewhere in the calculation. In most houses the condensing unit is that motor; if you have already entered it under air conditioning, leave the advanced field at zero rather than counting it twice.
Divide the total by 240 V for a standard 120/240 V three-wire service, or by 208 V for an apartment fed from a three-phase system, and you have the calculated load in amperes.
Worked example: a 2,000 ft² all-electric house
The house has 2,000 ft² of conditioned space, two small-appliance circuits, one laundry circuit, a 12 kW range, a 5 kW dryer, four fastened appliances totalling 8,100 VA (a 4,500 VA water heater, a 1,200 VA dishwasher, a 900 VA disposal and a 1,500 VA built-in microwave), 10 kW of electric baseboard heat and a 5 kVA condensing unit. The service is 120/240 V.
- General lighting. 3 VA/ft² × 2,000 ft² = 6,000 VA.
- Small-appliance and laundry. Three circuits × 1,500 VA = 4,500 VA.
- General subtotal. 6,000 + 4,500 = 10,500 VA.
- Apply Table 220.45. First 3,000 VA at 100% = 3,000. The remaining 7,500 VA at 35% = 2,625. General demand = 5,625 VA.
- Range. 12 kW falls in the 8¾–12 kW band, so Column C gives a flat 8,000 VA.
- Dryer. Nameplate 5,000 VA, and 220.54 sets a 5,000 VA floor, so 5,000 VA.
- Fastened appliances. Four of them, so 8,100 × 0.75 = 6,075 VA.
- Heating or cooling. 10,000 VA of heat against 5,000 VA of cooling; they cannot run together, so count 10,000 VA and drop the condenser.
- Total calculated load. 5,625 + 8,000 + 5,000 + 6,075 + 10,000 = 34,700 VA.
- Amperes. 34,700 ÷ 240 = 144.6 A.
A 150 A service covers it, with 150 − 144.6 = 5.4 A of headroom, or 3.6% of the rating — technically compliant and practically tight. Most contractors would install 200 A here, because the marginal cost at rough-in is small and the calculated load leaves no room for the EV charger this owner will want in three years. Run the same house through the EV charger circuit load calculator before you commit to 150 A.
Cooking appliance demand from Table 220.55, one appliance
| Nameplate rating | Rule that applies | Demand load |
|---|---|---|
| 1.75 kW or less | Below the table — count at nameplate | Nameplate VA |
| Over 1¾ but under 3½ kW | Column A, one appliance, 80% | 0.80 × nameplate |
| 3½ through 8¾ kW | Column B, one appliance, 80% | 0.80 × nameplate |
| 8.0 kW | Column B, one appliance, 80% | 6,400 VA |
| Over 8¾ through 12 kW | Column C, one appliance | 8,000 VA |
| 12 kW | Column C, one appliance | 8,000 VA |
| 14 kW | Column C + 5% × 2 | 8,800 VA |
| 16 kW | Column C + 5% × 4 | 9,600 VA |
| 18 kW | Column C + 5% × 6 | 10,400 VA |
| 24 kW | Column C + 5% × 12 | 12,800 VA |
| Over 27 kW | Outside the table | Calculate another way |
The Column A and Column B percentages shown are the one-appliance row; both fall as the appliance count rises. The 5% increments apply for each additional kilowatt or major fraction above 12 kW, so a 13.6 kW range takes two increments and a 13.4 kW range takes one.
How to read the answer
Compare the calculated amperes against the standard service ratings, and round up. Residential services come in 100, 125, 150, 175, 200, 225 and 400 A. 230.79(C) sets 100 A as the minimum service disconnect for a one-family dwelling regardless of how small the calculation comes out, so a tiny cabin still gets 100 A.
Watch the spare capacity figure. A calculated load that lands at 96% of the service rating passes inspection and then fails the owner. A 48 A EV charger is a continuous load counted at 125%, so it adds 60 A of calculated load on its own. If the calculated load uses more than 90% of the service rating, price the next size up before you order the meter can.
The service conductors are sized separately, and usually smaller than you expect. 310.12 lets you size the ungrounded service conductors for a one-family dwelling at 83% of the service rating for services from 100 A through 400 A, which is why a 200 A dwelling service is commonly run in 4/0 aluminum rather than 250 kcmil: 200 × 0.83 = 166 A, and 4/0 aluminum carries 180 A in the 75 °C column while a full 200 A would demand 250 kcmil. Take the calculated amperes to the wire size and ampacity calculator and then check the run length with the voltage drop calculator, because on a long rural service drop voltage drop, not ampacity, sets the wire size.
A calculated load below 100 A on an existing house does not mean the panel is fine. Load calculations say nothing about available breaker spaces, bus rating, the condition of the neutral, or whether the panel is one of the models no longer supported by any listed breaker. Those are inspection questions, not arithmetic questions.
Mistakes that make a dwelling calculation wrong
- Counting the range at nameplate. A 12 kW range contributes 8,000 VA, not 12,000. This single error adds nearly 17 A to a 240 V calculation and has sent more than one house to an unnecessary 200 A service.
- Including the garage and the unfinished basement in the floor area. The area is habitable space from outside dimensions. An unfinished basement counts only if it is adaptable for future use; an open porch and an attached garage never do.
- Adding heating and cooling together on a straight electric-furnace house. They are noncoincident under 220.60 and only the larger is counted. The mirror-image error is worse: leaving a heat pump's strip heat out when the controls let both run.
- Taking the 75% factor of 220.53 with three appliances. The permission requires four or more fastened-in-place appliances, and ranges, dryers and HVAC do not count toward that four.
- Forgetting the 5,000 VA floor on the dryer. A 4.4 kW dryer is still 5,000 VA in the worksheet.
- Applying Table 220.45 to appliance loads. The demand factors apply only to general lighting, small-appliance and laundry loads. Everything below that line is counted at its own rule.
Which edition of the NEC applies to you
This calculator follows NFPA 70, the National Electrical Code, 2023 edition. The demand factors and table structures used here are unchanged from the 2017 and 2020 editions, but the section numbering is not: the 2023 edition reorganised Article 220, so the general lighting rule moved from 220.12 to 220.41 and the lighting demand table moved from Table 220.42 to Table 220.45. Adoption is by state and sometimes by city, and several states still enforce the 2017 or 2020 edition. Cite the section numbers from the edition your jurisdiction has adopted, and confirm any local amendment — some jurisdictions require a minimum 200 A service for new dwellings regardless of the calculation.
Standard method, optional method, and the alternatives
The optional method of 220.82 exists because the standard method over-predicts modern houses. It takes 100% of the first 10 kVA of everything and 40% of the rest, then adds the largest HVAC figure. For an all-electric house it almost always gives a smaller answer, and it is far quicker. Its condition is that the dwelling is served by a single 120/240 V or 208Y/120 V set of three-wire service conductors of at least 100 A. Compare the two on the same house with the optional dwelling load calculation calculator.
For an existing dwelling with metered history, 220.87 is better than either. It lets you base the calculation on the maximum demand recorded over a 12-month period, multiplied by 125%, plus the new load. Utilities will usually supply interval data on request, and this is the argument that keeps many 100 A services alive when a heat pump goes in.
Multifamily buildings use a different table. Table 220.45 governs the dwelling unit itself, but the feeder and service to a building with several units uses the demand factors of 220.84, which fall steeply with the number of units. Do not scale a single-unit calculation by the number of apartments.
Once the service size is settled, the downstream work begins. Individual circuits are sized with the 125% continuous-load rule — that is the continuous load breaker sizing calculator. Feeders to subpanels use the same Article 220 machinery with the loads they actually serve. And if the house has a large motor load, size its protection with the motor overload and breaker sizing calculator rather than the general rules here.
Key terms
- Connected load
- The arithmetic sum of every nameplate on the premises. It is never the number you size a service to.
- Calculated load
- The connected load after Article 220's demand factors are applied. This is the legal basis for the service, feeder and conductor sizes.
- Demand factor
- The ratio of the maximum demand of a system to its total connected load — the code's way of recognising that not everything runs at once.
- Noncoincident loads
- Two or more loads that cannot be energised at the same time. 220.60 lets you count only the largest of them.
- Fastened in place
- Equipment secured to the structure, such as a water heater or a disposal, as opposed to a cord-and-plug appliance you could carry out of the house.