Eui Calculator

Background.

A utility bill tells you how much energy a building bought, but not whether that is a lot. A large hospital and a small dental office will never use similar amounts, and electricity arrives in kilowatt-hours while gas arrives in therms, so even the two bills for one building cannot simply be added together. Energy use intensity deals with both problems at once: convert every fuel to the same unit, add them, and divide by floor area.

In the United States the convention, set by the EPA's ENERGY STAR Portfolio Manager, is thousands of British thermal units per square foot per year, written kBtu/ft². A kilowatt-hour is 3.412 kBtu and a therm is 100 kBtu by definition, so one therm of gas holds as much energy as about 29.3 kWh. In the worked example below, 100,000 kWh beside 5,000 therms looks like a 20-to-1 split on paper, yet gas supplies about 59% of the energy.

The figure produced here is site EUI: energy counted at the meter, exactly as the bills record it. It is the number facility managers track year over year, and the one to check when you want to know whether a lighting retrofit or a new boiler made a difference in the same building.

Three things are left out on purpose. Fuels other than electricity and natural gas, such as fuel oil, propane or district steam, have no input, so a building that burns them will read low. Source energy, which adds the losses at power plants and on the grid, is not computed. And there is no weather normalization, so a harsh winter pushes gas use and the EUI up without anything having changed inside the building.

What is eui calculator?

Site energy use intensity is a building's total annual energy consumption, as measured at its own meters, divided by its gross floor area. Here the total is electricity plus natural gas, both expressed in kBtu, so the result is kBtu per square foot per year. Gross floor area in the ENERGY STAR sense is the whole enclosed area of every floor, measured to the outside surfaces of the exterior walls, corridors, stairwells and plant rooms included. Parking areas are not counted in it.

How to use this calculator.

1. 01Add up twelve consecutive months of electricity from the bills and enter the total in Annual electricity use. Use the kWh consumption line, not the kW demand figure that some commercial bills also show.
2. 02Do the same for gas in Annual natural gas use. If the utility bills in CCF (hundreds of cubic feet), multiply by the therm factor printed on the bill to get therms before entering it.
3. 03Enter Gross floor area in square feet, measured to the outside of the walls and including every floor, but leaving out parking. If you only have square metres, multiply by 10.764.
4. 04Compare the site EUI first with the same building's earlier years. Set it against other buildings only when they share a use type and a similar climate.

The formula.

Site EUI = (E × 3.412141633 + G × 100) ÷ A, where E is annual electricity in kWh, G is annual natural gas in therms and A is gross floor area in square feet. The 3.412141633 is the number of kBtu in one kilowatt-hour: a kWh is 3,600 kJ and a Btu is about 1.055 kJ. The 100 follows from the therm being defined as 100,000 Btu. The bracketed sum is the annual site energy, reported on its own in kBtu, and dividing by area turns it into an intensity. Because the result is a ratio, the floor area matters as much as the bills: entering 10% too little area makes the EUI about 11% too high. Neither fuel is weighted for how it was generated or delivered, which is what separates site EUI from source EUI.

A worked example.

Frequently asked questions.

References& sources.

1. [1]U.S. Environmental Protection Agency ENERGY STAR. Portfolio Manager technical reference current 2026. Energy use intensity definitions. Retrieved 2026-08-06.
2. [2]National Institute of Standards and Technology. NIST SI Guide, 2008 edition. Appendix B unit relationships. Retrieved 2026-08-06.
3. [3]OpenStax, Rice University. University Physics, 2016. Volume 1 mechanics and Volume 2 thermodynamics. Retrieved 2026-08-06.