Calculate a building’s Energy Performance Index from annual energy use and floor area, or estimate annual energy from EPI and area in kWh/m²/yr.
Energy Performance Index Formula
The energy performance index, or EPI, measures annual energy use per unit of building floor area. This calculator reports the main result in kWh/m²/year and also shows the equivalent value in kWh/ft²/year.
- EPI = energy performance index
- E = annual energy consumption in kWh/year
- A = building floor area in m² or ft²
For the metric result, the calculator uses:
For the square-foot result, the calculator uses:
If you enter energy or area in another supported unit, the calculator converts the input before calculating EPI:
The annual energy consumption field supplies the numerator of the formula. The building floor area field supplies the denominator. The optional benchmark field does not change the EPI result. It compares your calculated EPI against a target value in kWh/m²/year and shows whether the result is higher, lower, or equal to that benchmark.
Comparing energy performance
Raw EPI does not assign a universal efficiency grade. Compare similar building types, climate, occupancy and operating hours on the same site or source energy basis. Whole-building site intensity requires all site energy sources and matching gross floor area. This calculator does not normalize weather or calculate an ENERGY STAR score.
Energy and Area Conversion Factors
Btu uses the International Table definition: 1055.05585262 J. The original therm factor below is the U.S. therm (105480400 J); the calculator also offers the EC therm (105506000 J, or 29.30722222 kWh). Select the convention matching your energy data. One kWh is 3600000 J.
| Input unit | Converted unit used in the calculation | Conversion |
|---|---|---|
| kWh/year | kWh/year | No conversion needed |
| MWh/year | kWh/year | Multiply by 1,000 |
| BTU/year | kWh/year | Divide by 3,412.141633 |
| Therms (U.S.)/year | kWh/year | Multiply by 29.300111 |
| Square feet | Square meters | Multiply by 0.09290304 |
Example Calculations
Example 1: EPI from kWh and square meters
You have a building that uses 120,000 kWh per year and has a floor area of 1,000 m².
The energy performance index is 120 kWh/m²/year.
Example 2: EPI from MWh and square feet
You have a building that uses 250 MWh per year and has a floor area of 20,000 ft².
The energy performance index is about 134.55 kWh/m²/year. The same result is also equal to 12.50 kWh/ft²/year.
FAQ
What does a lower energy performance index mean?
A lower EPI means the building uses less energy per unit of floor area. In general, that indicates better energy performance. However, EPI should be compared with similar buildings because operating hours, climate, occupancy, equipment, and building type can strongly affect energy use.
Should floor area include all spaces in the building?
Use the floor area that matches the energy consumption you entered. If the annual energy figure covers the whole building, use the whole building floor area. If the energy figure covers only a tenant space, floor, or specific zone, use only that same area. Mixing whole-building energy with partial area, or partial energy with whole-building area, will give a misleading EPI.
How do I use the benchmark value?
Enter a benchmark in kWh/m²/year when you have a target or reference EPI. The calculator compares your result with that value and reports the percentage difference. For example, if your EPI is 120 and the benchmark is 100, the result is 20% higher than the benchmark.
