Load Calculation Calculator
Free electrical load calculation tool for residential and commercial buildings. Calculate service entrance sizing, panel loads, demand factors, and ensure NEC Article 220 compliance.
Calculation Method
Load Components
Calculation Details
Results
Residential Loads (NEC 220)
Commercial Loads
Demand Factors
- Lighting: First 3000 VA @ 100%
- Lighting: Remainder @ 35%
- Electric ranges: Use Table 220.55
- Motors: 125% of largest motor
- HVAC: 100% of largest load
Standard Method (220.82)
Load = Area × 3 VA/sq ft
First 3000 VA @ 100%
Remainder @ 35%
I = Total Demand Load / Voltage
Optional Method (220.83)
Sum all connected loads
First 10 kVA @ 100%
Remainder @ 40%
Add 100% of largest HVAC load
Example Calculation
2000 sq ft residence with standard loads:
• General lighting: 2000 × 3 = 6000 VA
• Small appliance: 2 × 1500 = 3000 VA
• Laundry: 1500 VA
• Total: 10,500 VA
• First 3000 VA @ 100% = 3000 VA
• Next 7500 VA @ 35% = 2625 VA
• Subtotal: 5625 VA
• Add range (8000 VA demand) + dryer (5000 VA) + water heater (4500 VA)
• Total demand: 23,125 VA ÷ 240V = 96.4A → 100A minimum service
How to Calculate Electrical Load: Step-by-Step
A proper load calculation determines the total electrical demand for a building. This is essential for sizing services, panels, and feeders per NEC Article 220.
Step 1: Calculate General Lighting Load
Multiply the total square footage by 3 VA per square foot per NEC Table 220.12. For a 2,000 sq ft home, this equals 6,000 VA. This covers all general-use receptacles and lighting outlets.
Step 2: Add Small Appliance and Laundry Circuits
Add 1,500 VA for each small appliance circuit (minimum two required) and 1,500 VA for the laundry circuit. That is 4,500 VA for a typical home with two kitchen circuits and one laundry circuit.
Step 3: Include Fixed Appliance Loads
Add the nameplate VA rating for each permanently connected appliance: water heater, dryer, range, dishwasher, and disposal. If you have four or more fixed appliances, you can apply a 75% demand factor.
Step 4: Apply NEC Demand Factors
For general lighting and receptacle loads, the first 3,000 VA is at 100%, and the remainder is at 35% per NEC Table 220.42. Apply the appropriate demand factors for ranges, dryers, and HVAC loads.
Step 5: Convert to Amps
Divide the total demand VA by the system voltage (240V for single-phase residential) to find the service amperage required. Select the next standard service size: 100A, 150A, or 200A.
Formula
Service Amps = Total Demand VA / System Voltage
Where: Total Demand VA = Sum of all loads after applying NEC demand factors, System Voltage = 240V for single-phase residential
Worked Example
Scenario: Calculate the service size for a 2,000 sq ft home with electric range, dryer, water heater, dishwasher, and 3-ton AC.
- Step 1: General lighting: 2,000 x 3 = 6,000 VA
- Step 2: Small appliance + laundry: 4,500 VA. Subtotal = 10,500 VA
- Step 3: Fixed appliances: Range 8,000 + Dryer 5,000 + WH 4,500 + DW 1,200 = 18,700 VA
- Step 4: Lighting demand: 3,000 at 100% + 7,500 at 35% = 5,625 VA. Range at 8,000 VA (Table 220.55). AC: 5,000 VA at 100%
- Step 5: Total demand approx 30,525 VA / 240V = 127A. Select 150A or 200A service
Result: This 2,000 sq ft home needs a minimum 150A service, though 200A is recommended for future capacity.
Load Calculation Questions & Answers
Do I really need to do a load calculation for every job?
For service upgrades, panel changes, and new construction - absolutely. For adding a single outlet or light fixture, probably not. But when you're upgrading from 100A to 200A service, the inspector wants to see that the house actually needs it. I've seen too many failed inspections because someone skipped the load calc and couldn't justify the service size.
Why is my calculated load so much higher than my actual electric bill?
Load calculations assume worst-case scenario - everything running at once. Your electric dryer, water heater, A/C, and oven rarely all run simultaneously at full load. The calculation ensures your service can handle peak demand, but your typical usage is much lower. That's why demand factors exist - they account for realistic usage patterns.
What's the difference between connected load and calculated load?
Connected load is everything added up at nameplate ratings - if you have 50kW of equipment, that's your connected load. Calculated load applies demand factors per NEC 220. A house might have 40kW connected load but only 25kW calculated load after applying residential demand factors. You size the service for calculated load, not connected.
Can I use the optional method for all residential load calculations?
Only if the dwelling has electric heat or A/C over 10kW, and total connected load exceeds 10kW. The optional method in NEC 220.82 usually gives you a smaller service size, but you have to meet the requirements. For simple houses without electric heat, stick with the standard method in NEC 220.40-220.61. When in doubt, calculate both ways and use whichever gives the smaller result.
How do I handle a house with both gas and electric appliances?
Only count the electric loads in your calculation. Gas furnace with electric blower? Count just the blower motor (usually 10-15 amps). Gas water heater? Zero electrical load. Gas range with electric ignition? Count maybe 500 watts for controls and lights. Don't double-count - if it runs on gas, the electrical load is usually minimal.
What's the deal with 125% for continuous loads?
Any load expected to run for 3+ hours needs to be calculated at 125% of its nameplate current. This mainly affects lighting circuits, and some motor loads. A 16-amp continuous load becomes 20 amps for calculation purposes. Most residential loads aren't continuous except lighting, but commercial buildings have lots of continuous loads.
Do electric vehicle chargers count as appliance loads?
Yes, and they're typically continuous loads at their maximum rating. A 40-amp Level 2 charger needs to be calculated at 50 amps (40 × 125%). Some newer chargers have demand response features that can reduce load, but unless you have specific load management equipment, calculate at full nameplate. EVs are becoming a major factor in residential load calculations.
Can I count diversity factors between different panels?
Not really in residential work. NEC demand factors apply to the service calculation, but you can't say "Panel A won't run when Panel B is running" and reduce your feeder sizing. Each panel feeder needs to be sized for its actual load. In large commercial buildings with load monitoring, you might have more options, but residential is pretty straightforward.
What if the customer wants to add more stuff later?
Size for what they have now plus any definite future additions. Don't oversize "just in case" - you'll price yourself out of the job. But if they're planning a hot tub next year, include it. Many electricians add 20-30% to their calculation as a practical matter, but code-wise you only need to meet current requirements.
Why do commercial load calculations seem so much more complicated?
More equipment types, more motor loads, and fewer demand factors to help you out. Residential has generous demand factors because homes have predictable usage patterns. Commercial buildings might run most equipment simultaneously, so you can't count on much diversity. Plus you have to deal with power factor, harmonic loads, and equipment that cycles on and off.
What's the most common load calculation mistake?
Forgetting to include the general lighting load properly. You need 3 VA per square foot minimum, but you also need to count actual lighting circuits. Some electricians double-count by including both the 3 VA/sq ft and then adding individual lighting circuits on top. Read NEC 220.12 carefully - the 3 VA/sq ft covers general lighting, then you add specific heavy-duty lighting separately.
Can I use nameplate ratings from old appliances?
Use what's actually installed. That 1990s electric range might be rated 12kW but if it's staying, use 12kW in your calculation. New appliances often have better efficiency, so a new range might only be 9kW. Don't assume - check the actual nameplate on equipment that's staying, and get specs for new equipment. Energy Star appliances can significantly reduce your calculated load.
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