Residential Load Calculation, Step by Step (2020 NEC Standard Method)

This question is from JCR's 500+ question mock exam. 67% of students got this wrong. Try it with your code book open, then check your answer below.

The standard method in brief

A residential load calculation (for a dwelling unit, in NEC terms) uses the standard method in Part III of Article 220 of the 2020 NEC (NFPA 70). Add the general lighting load (3 VA per square foot), the small-appliance and laundry circuits, and apply the Table 220.42 demand factors. Then add the range, the dryer, the fixed appliances, and the larger of the heating or air-conditioning load. Divide the total by 240 V to get the minimum service size in amps.

Most misses on load calculations come from skipped steps, not hard math. Follow the order below every time.

Residential load calculator (standard method)

Enter your house's numbers. The calculator follows the eight steps below and rounds up to the next standard service size. It opens with the 2,000 sq ft worked example filled in.

Step 1: General lighting load

Multiply the floor area by 3 VA per square foot. In the 2020 NEC, the dwelling unit load is in 220.14(J). Table 220.12 now covers non-dwelling occupancies only.

Figure the floor area from the outside dimensions. For dwelling units, don't count open porches, garages, or unused or unfinished spaces not adaptable for future use (220.11).

The 3 VA already covers three groups of outlets, so don't add separate loads for them (220.14(J)):

• General-use receptacles rated 20 A or less, including those on the bathroom and garage circuits in 210.11(C)(3) and (C)(4)
• The outdoor receptacles in 210.52(E) and the basement, garage and accessory building receptacles in 210.52(G)
• The lighting outlets in 210.70

Step 2: Small-appliance and laundry circuits

Add 1500 VA for each 2-wire small-appliance branch circuit (220.52(A)) and 1500 VA for each 2-wire laundry circuit (220.52(B)). A dwelling needs two or more 20-ampere small-appliance circuits (210.11(C)(1)) and at least one 20-ampere laundry circuit (210.11(C)(2)), so the minimum is 4500 VA.

These loads may be added to the general lighting load and put through the same demand factors.

Step 3: Apply Table 220.42

For dwelling units:

• First 3000 VA at 100%
• 3001 to 120,000 VA at 35%
• Over 120,000 VA at 25%

Step 4: Range

Use Table 220.55, not the nameplate. The table is permitted, not required, but exam answers use it. For one household range rated 12 kW or less, Column C gives 8 kW. For a range over 12 kW (up to 27 kW), Note 1 increases the Column C value by 5% for each additional kW, or major fraction of a kW, over 12.

Step 5: Dryer

Use 5000 W (VA) or the nameplate rating, whichever is larger (220.54). One to four dryers are taken at 100% (Table 220.54).

Step 6: Fixed appliances

With four or more appliances fastened in place, each rated ¼ hp or more or 500 W or more, on the same feeder or service, you may take 75% of their total nameplate load (220.53). Leave out household cooking equipment fastened in place, clothes dryers, space heating and air conditioning. They have their own rules.

If any of these appliances has a motor, add another 25% of the largest motor load (220.50 and 430.24). The NEC's own example in Informative Annex D, Example D1(b), does this.

Step 7: Heat or air conditioning, not both

Fixed electric space heating is taken at 100% of the connected load (220.51). Heat and air conditioning are noncoincident loads, so you may use only the larger of the two (220.60).

Step 8: Convert to amps

Divide the total VA by 240 V. The service disconnect must be rated at least that much (230.79), and never less than 100 A, 3-wire, for a one-family dwelling (230.79(C)).

Worked example: 2,000 sq ft house

35,575 VA ÷ 240 V = 148.2 A. Minimum service: 150 A.

The six mistakes behind most wrong answers

1. Applying Table 220.42 before adding the small-appliance and laundry circuits.
2. Using the range nameplate when the question expects Table 220.55.
3. Adding both heat and air conditioning.
4. Taking 75% with only three fixed appliances.
5. Putting the range, a built-in microwave or other cooking equipment, or the dryer in the fixed-appliance group.
6. Forgetting the extra 25% for the largest motor (220.50 and 430.24).

Article 220 also has an optional method for dwellings (220.82) that often gives a smaller result. Exam questions tell you which method to use. Read the question twice.

Want more practice? Try JCR's free 25-question practice exam.

Common questions

How many VA per square foot for a house?

3 VA per square foot for the general lighting load in a dwelling (220.14(J)). That number also covers general-use receptacles and lighting outlets, so you don't add them separately.

Do you count the garage in the square footage?

No. Leave out open porches, garages, and unused or unfinished spaces that can't be adapted for future use (220.11). Measure from the outside dimensions.

When can you take 75% for appliances?

When there are four or more appliances fastened in place on the same feeder or service, each ¼ hp or 500 W or more (220.53). Fastened-in-place cooking equipment, dryers, space heating and air conditioning don't count toward the four.

What size service does a 2,000 sq ft house need?

It depends on the loads. In JCR's worked example, a 2,000 sq ft house with a 12 kW range, a 5.5 kW dryer, four fixed appliances and 10 kW of heat comes to 35,575 VA, or 148.2 A, so a 150 A service.

All section numbers here are from the 2020 NEC. Order the 2020 NEC book, or read it online with a paid NFPA LiNK subscription. To confirm which edition your exam uses, check our state requirements page.

JCR checked these steps and section numbers against the 2020 NEC in NFPA LiNK on October 21, 2026.

Related: Continuous loads and 100%-rated breakers (210.20(A)) · Sizing the main bonding jumper at the service

Free video: services and load calculations

Victor walks through the NEC articles behind a rough-in, including feeders, services and load calculations: watch the lesson on YouTube. More free lessons on JCR's channel.

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The JCR manual and videos work dwelling and service calculations step by step, so you follow the same order every time on the exam.

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