Kilowatt-Hours vs. MMBtu—Metrics for Measuring Energy Use – GreenBuildingAdvisor

By RANDY WILLIAMS | September 25, 2025

When looking at a building’s energy consumption, we quickly bump into units. Utility bills, energy models, and rating-system requirements all talk about kilowatt-hours, Btu, therms, and MMBtu. The numbers can look wildly different for the same building simply because they can be expressed in different ways.

I’ve spent enough time working with energy-use metrics to see how the units chosen shape people’s understanding. Homeowners relate to kilowatt-hours because that’s what appears on their electric bills. Auditors and program administrators often prefer MMBtu because it puts all fuels on the same footing. Both units have their place, but knowing what each means and when to use each will lead to clearer communication and a better understanding for the customer.

Two Common Energy Metrics

Kilowatt-hours

A kilowatt-hour (kWh) is the basic unit of electric energy. One kilowatt-hour is one kilowatt of power used for one hour—running a 1,000-watt hair dryer for an hour, or ten 100-watt old-school light bulbs for an hour. It’s the unit of energy an electric utility charges for, and it’s the unit most homeowners are familiar with.

The kilowatt-hour works well whenever we are talking strictly about electricity: lighting, appliances, heat pumps, or electric vehicles. The scale is more easily understood; a typical U.S. home might use 10,000 to 12,000 kWh per year for everything, or 3,000 to 5,000 kWh per year just for heating with a cold-climate heat pump.

That being said, when I estimate a homeowner’s total energy use, I will convert non-electric energy (gas, fuel oil, wood, etc.) to the kWh metric, just so the homeowner isn’t confused by the MMBtu metric.

MMBtu

MMBtu stands for one million British thermal units (the “M” is the Roman numeral for thousand, “MM” denotes one thousand-thousand or one million; “Btu” is British…