Necresidential Load Calculator
Estimate necresidential load for your project with our free calculator. Get accurate material quantities, costs, and specifications.
Reviewed by Abdullah, Technical Content Specialist
Formula
Service Amps = Total Demand Load (VA) / 240V
The NEC standard method calculates total demand by applying 3 VA/sq ft for general lighting, adding small appliance and laundry circuits at 1,500 VA each, applying demand factors (100% for first 10,000 VA, 40% for remainder), then adding individual appliance demands. The total demand in VA divided by 240V gives the minimum service amperage.
Worked Examples
Example 1: 2,500 sq ft Home
Problem:Calculate service size for a 2,500 sq ft home with 12 kW range, 5.5 kW dryer, 4.5 kW water heater, 5 kW AC, and 10 kW heat strips.
Solution:General lighting: 2,500 x 3 = 7,500 VA\nSmall appliance: 2 x 1,500 = 3,000 VA\nLaundry: 1,500 VA\nTotal general: 12,000 VA\nDemand: 10,000 + (2,000 x 0.4) = 10,800 VA\nRange: 8,000 VA | Dryer: 5,500 VA\nHVAC (larger): max(5,000, 10,000 x 0.65) = 6,500 VA\nTotal: 10,800 + 8,000 + 5,500 + 6,500 + 4,500 = 35,300 VA\nAmps: 35,300 / 240 = 147 A
Result:147 A demand | 150A or 200A service recommended
Example 2: 1,500 sq ft Condo
Problem:Calculate service size for a 1,500 sq ft condo with 8 kW range, no dryer, 3 kW water heater, and 3.5 kW AC.
Solution:General: 1,500 x 3 = 4,500 VA + 3,000 + 1,500 = 9,000 VA\nDemand: 9,000 x 1.0 = 9,000 VA (under 10,000)\nRange: 8,000 VA\nHVAC: 3,500 VA\nTotal: 9,000 + 8,000 + 3,500 + 3,000 = 23,500 VA\nAmps: 23,500 / 240 = 97.9 A
Result:98 A demand | 100A service minimum
Frequently Asked Questions
What is an NEC residential load calculation?
An NEC residential load calculation follows the procedure outlined in the National Electrical Code (NEC) Article 220 to determine the minimum electrical service size for a dwelling unit. The calculation accounts for general lighting loads at 3 VA per square foot, small appliance circuits at 1,500 VA each (minimum two required), laundry circuit at 1,500 VA, and all major appliance loads. Demand factors are then applied to reduce the calculated load to reflect the fact that not all loads operate simultaneously. This calculation is required for every new home and service upgrade permit.
How do I calculate the load-bearing capacity of a beam?
Beam capacity depends on material, cross-section dimensions, span length, and support conditions. For a simple rectangular wood beam, bending strength = (F_b x b x d^2) / 6, where F_b is allowable stress, b is width, and d is depth. Always consult a structural engineer for critical applications.
References
Reviewed by Abdullah, Technical Content Specialist · Editorial policy