Service Load Calculator

About the Service Load Calculator

Estimates the minimum electrical service (amps) for a dwelling from general lighting, appliance and HVAC loads using a simplified standard-method approach.

How to use this calculator

1. Enter the dwelling details, such as square footage and the major electrical loads.
2. Include general lighting, small-appliance, laundry, and any fixed appliances or heating loads if the calculator asks for them.
3. Check whether the calculator applies demand factors, because not every load is counted at full value.
4. Review the final recommended service size and compare it with standard service ratings like 100 A, 150 A, or 200 A.

The formula explained

The calculator estimates the total electrical demand in amperes or volt-amperes by combining the listed loads and then applying the appropriate demand factors. The result is used to suggest a suitable service size for the dwelling.

• n = the number of load items or appliances being counted
• A = amperes, a unit of electrical current
• V = volts, the electrical pressure used in the service
• VA = volt-amperes, a unit used for electrical load

Step by step method

1. List the dwelling loads, such as general lighting, appliances, and heating or cooling equipment.
2. Add the loads according to the calculator rules, then apply any demand factors if required.
3. Convert the total load into an estimated service current, then compare it with standard service sizes.

Worked example

Problem. A house has a calculated load of 48{,}000 VA on a 240 V service. What is the estimated service current?

1. Use the relation I = VA f7 V.
2. Substitute the numbers, I = 48{,}000 f7 240.
3. Compute the result, I = 200 A.

Tips and common mistakes

• Do not count every appliance at full capacity unless the method specifically says to, because demand factors often reduce the total.
• Make sure to use the correct voltage for the dwelling service, because 120 V and 240 V systems give different current results for the same load.

Frequently asked questions