🏢 EUI Calculator

How to Use This Calculator

Enter the building's annual electricity in kWh and natural gas in therms (both on the utility bills), the gross floor area in square feet, and the building type. The calculator converts everything to kBtu, divides by area, and reports site EUI with a benchmark comparison for your building type. If you have other fuels like oil or propane, convert them to kBtu first (oil is about 138,500 kBtu per gallon, propane about 91,500) and add them to the gas figure mentally, or just note the result runs slightly low.

The Method: All Energy Over All Area

The conversions are definitions: one kWh equals 3.412 kBtu by the physics of energy units, and one therm of natural gas is defined as 100 kBtu. Dividing by floor area normalizes for size, which is what makes EUI the standard benchmarking metric instead of raw bills. The worked example gives 37.1, comfortably below the office median, suggesting an efficient building or mild climate. Building type matters because use patterns differ wildly: a restaurant's cooking load makes its EUI several times an office's, so the calculator benchmarks within type. Site EUI is reported because it reflects what you pay for and can reduce; source EUI adds generation losses and is the ENERGY STAR scoring basis.

Worked Example

A 10,000 sq ft office uses 50,000 kWh of electricity and 2,000 therms of gas in a year. Electricity: 50,000 x 3.412 = 170,600 kBtu. Gas: 2,000 x 100 = 200,000 kBtu. Total = 370,600 kBtu. EUI = 370,600 / 10,000 = 37.1 kBtu per sq ft per year. Against the office median near 65, this building runs about 43 percent better than typical. In metric: 37.1 x 3.154 = 117 kWh per sq m per year. Enter those inputs above and the calculator reproduces every figure, including the benchmark verdict.

Benchmarks by Building Type

Offices cluster around a median near 65, with efficient ones under 40. Homes typically run 40 to 60, heavily climate-driven. Schools land near 50 to 70 with their intermittent schedules. Retail varies with lighting intensity. Warehouses are the efficiency champions by this metric, often under 20, because vast floor areas divide modest heating loads. Restaurants and hospitals sit far above offices and need their own benchmarks. The lesson: never compare across types. A 50 EUI is excellent for a school and mediocre for a warehouse.

From Number to Action

EUI tells you where you stand; an energy audit tells you why. If EUI runs high, the usual culprits in order are HVAC scheduling (running unoccupied hours), simultaneous heating and cooling, lighting left on, and envelope leaks. The cheapest fixes are controls: setpoints, schedules, and sensors routinely cut 10 percent for near-zero cost. Equipment upgrades follow at natural replacement time, when the incremental cost of efficiency is smallest. Recompute EUI yearly from the same bills; the trend line is the real report card, and weather-normalize mentally before celebrating or panicking.

ENERGY STAR Scores and Benchmarking

EUI is the raw physics; the ENERGY STAR score (1-100) is the percentile ranking against similar buildings, and it is what tenants and buyers actually read. A score of 75+ earns certification and the plaque; the score normalizes for weather, occupancy, and operating hours, so a hospital is not compared to a warehouse. Benchmarking ordinances in major cities now require annual reporting: New York's Local Law 84, and similar rules in dozens of cities, publish building EUIs publicly. A poor public score pressures owners to retrofit; a good one markets itself. To benchmark, enter 12 months of utility data into ENERGY STAR Portfolio Manager (free); it computes both EUI and score. Track year over year: the trend line is what efficiency programs and buyers want to see, more than any single number.

Driving EUI Down: The Biggest Levers

For most commercial buildings, HVAC is half the EUI or more, so it dominates retrofit math. The ranked measures by typical payback: LED lighting with controls (1-3 years), building automation tune-ups and scheduling fixes (under a year; many buildings heat and cool simultaneously due to bad controls), high-efficiency rooftop units at replacement time, and envelope improvements (slow payback, do with other renovations). Before spending, fix operations: simultaneous heating and cooling, lights on all night, and ventilation running in empty buildings are free to correct and shockingly common. Recommissioning studies routinely find 10-20 percent savings from controls alone. This calculator establishes the baseline; the audit finds the waste; the trend line proves the fix.

A Second Worked Example: The Small Retail Shop

A 2,500-square-foot shop: 30,000 kWh of electricity and 500 therms of gas a year. kBtu: 30,000 times 3.412 is 102,360, plus 500 times 100 is 50,000, totaling 152,360. EUI: 152,360 divided by 2,500 is 60.9 kBtu per square foot per year. Against a retail median in the 60s to 80s depending on subtype, this shop sits at the efficient end. The lighting load dominates small retail, so the number responds fast to an LED retrofit.

Compare with the page's office example at 37.1: different building types, different medians, no direct comparison. Benchmark within type or the number misleads. A 60.9 retail shop can be efficient while a 60.9 office would be poor.

Site vs. Source EUI

Site EUI counts the energy at the building meter: what you pay for and can reduce. Source EUI adds the generation and transmission losses behind the meter, roughly tripling electricity's contribution since power plants discard about two-thirds of fuel energy as heat. ENERGY STAR scores use source EUI because it reflects total resource consumption; your utility bill uses site.

Electrification changes the comparison. A building switching from gas heat to heat pumps sees site EUI drop sharply, since heat pumps move heat instead of making it, while source EUI accounting gets complicated by the grid's fuel mix. Track both when fuel-switching, and report the one your audience expects.

Common EUI Mistakes

First: the wrong area. Gross floor area includes all conditioned floors; using leasable area or omitting the basement skews the result. Measure consistently. Second: the missing fuel. Counting electricity while forgetting the gas bill understates EUI; gather all 12 months of every fuel.

Third: cross-type comparison. Restaurants, offices, and warehouses live on different scales; compare against your type's median or the benchmark is meaningless. Fourth: ignoring weather. A harsh winter inflates heating EUI; weather-normalized comparisons use degree days. Fifth: the vacant-space distortion. A half-empty building divides full-building energy over occupied area wrongly; EUI assumes normal occupancy, so note the vacancy.