EUI Calculator: Energy Use Intensity for Buildings
Enter your building's annual energy consumption and floor area to get its Energy Use Intensity (EUI), the standard metric used by ENERGY STAR and the U.S. DOE to compare building efficiency. Switch between site energy sources (electricity, natural gas, fuel oil, propane), choose your building type to see how you rank against the national median, and get a CO2 emissions estimate alongside your EUI in both imperial (kBtu/ft²/yr) and metric (kWh/m²/yr) units. The steps panel shows every conversion so you can verify the math.
Formula
Worked example
A 10,000 ft² office uses 150,000 kWh of electricity and 800 therms of natural gas annually. Electricity: 150,000 × 3.412 = 511,800 kBtu. Gas: 800 × 100 = 80,000 kBtu. Total: 591,800 kBtu. EUI = 591,800 ÷ 10,000 = 59.2 kBtu/ft²/yr, which is below the national median of 77 for small offices and near the efficient threshold of 45.
What is Energy Use Intensity (EUI)?
Energy Use Intensity (EUI) is the standard metric used to measure and compare building energy performance. It equals total annual site energy consumption divided by the building's conditioned floor area, expressed in kBtu per square foot per year (or kWh/m²/yr in metric countries). A lower EUI means a more efficient building. The U.S. Department of Energy and ENERGY STAR use EUI as the primary yardstick for benchmarking commercial and institutional buildings against national averages. Because it normalizes for size, EUI makes it meaningful to compare a 2,000 ft² boutique office with a 200,000 ft² corporate campus: the one using less energy per unit of area is operating more efficiently, regardless of absolute consumption.
How to calculate EUI: formula and unit conversions
The formula is straightforward: EUI = Total site energy (kBtu) / Conditioned floor area (ft²). The conditioned floor area is the heated and/or cooled space; it excludes unconditioned storage, parking garages, and mechanical rooms.
The trickier part is converting all energy sources to a common unit (kBtu) before summing them. Use these standard factors:
- Electricity: 1 kWh = 3.412 kBtu
- Natural gas: 1 therm = 100 kBtu
- Fuel oil (No. 2): 1 gallon = 138.5 kBtu
- Propane: 1 gallon = 91.5 kBtu
To convert to the metric standard (kWh/m²/yr), multiply the kBtu/ft²/yr result by 3.15459. The ENERGY STAR Portfolio Manager tool accepts these same unit inputs and performs identical conversions.
How to interpret your EUI and compare it to benchmarks
The U.S. Commercial Buildings Energy Consumption Survey (CBECS) provides national median EUI values by building type, which serve as the primary benchmark. As a rule of thumb, a building in the top quartile of efficiency for its type typically earns an ENERGY STAR score of 75 or higher and is eligible for certification.
Key context for interpreting your number:
- Climate zone: Buildings in hot or cold climates naturally use more energy for heating and cooling. ENERGY STAR Portfolio Manager applies a weather-normalization adjustment; this calculator uses unadjusted national medians.
- Occupancy and hours: A 24/7 data center has a higher EUI than an identical building used only 8 hours per day. Compare within your operational profile when possible.
- Building age: Pre-1980 construction typically shows EUI 30-50% higher than post-2010 peers of the same type, reflecting improvements in codes, equipment, and envelope standards.
- Net-zero targets: The Architecture 2030 Challenge sets a pathway to net-zero energy by 2030. Office buildings aiming for this target typically need EUI below 20 kBtu/ft²/yr with on-site renewables, or below 30-35 before solar offsets.
CO2 emissions and the link between EUI and carbon
EUI measures site energy - the energy crossing the building's meter boundary. CO2 emissions depend on the type of fuel: electricity carries the carbon intensity of the grid (which varies by region and time of day), while combustion fuels have fixed emission factors. This calculator uses:
- Electricity: 0.0562 kg CO2/kBtu (US EPA eGRID 2022 national average, ~196 g CO2/kWh)
- Natural gas: 0.0530 kg CO2/kBtu
- Fuel oil No. 2: 0.0738 kg CO2/kBtu
- Propane: 0.0636 kg CO2/kBtu
Buildings in states with cleaner grids (California, New England, Pacific Northwest) have lower electricity emission factors than this national average. For a more precise carbon footprint, use your utility's region-specific eGRID sub-region factor from the EPA website.
How to reduce your building's EUI
EUI improvements typically come in three tiers, roughly ordered by cost-effectiveness:
- Operational changes (low/no cost): Adjusting thermostat setpoints, occupancy schedules, and plug-load policies. Buildings with advanced controls often cut EUI 5-15% with no capital investment.
- Equipment upgrades (medium cost): LED lighting retrofits, high-efficiency HVAC replacement, and variable-frequency drives on motors and fans are the most common measures. LED alone can cut lighting energy 50-70%.
- Envelope improvements (high cost, long payback): Adding insulation, upgrading windows, and air-sealing reduce heating and cooling loads. Most cost-effective during planned renovations.
An ASHRAE Level 1 energy audit (walk-through) typically costs $0.05-0.15/ft² and identifies the highest-return measures. An ASHRAE Level 2 audit adds detailed energy modeling and is required for major capital decisions.
EUI benchmarks by building type (CBECS 2018, US national medians)
| Building type | National median EUI (kBtu/ft²/yr) | Efficient threshold | Poor threshold |
|---|---|---|---|
| Office (Small) | 77 | 45 | 120 |
| Office (Large) | 94 | 55 | 145 |
| Retail / Strip Mall | 93 | 50 | 140 |
| K-12 School | 73 | 40 | 115 |
| Hospital / Healthcare | 234 | 150 | 350 |
| Hotel / Lodging | 102 | 65 | 160 |
| Warehouse | 36 | 18 | 70 |
| Multifamily Housing | 45 | 25 | 80 |
| Restaurant / Food Service | 263 | 160 | 400 |
| Other / Mixed Use | 80 | 45 | 130 |
Source: U.S. DOE Commercial Buildings Energy Consumption Survey 2018. "Efficient" is roughly the 25th-percentile EUI for that type.
Frequently asked questions
What is a good EUI for an office building?
The national median EUI for small office buildings is about 77 kBtu/ft²/yr and 94 for large offices (CBECS 2018). An efficient office typically achieves 45-55 kBtu/ft²/yr, and ENERGY STAR-certified offices generally score below 50. Net-zero-ready offices target 20-35 kBtu/ft²/yr before renewable energy offsets. Lower is always better.
What is the difference between site EUI and source EUI?
Site EUI measures energy at the building's meter - what you actually pay for. Source EUI accounts for the energy lost generating and delivering electricity, making it 2-3x higher for electrically dominated buildings (the US national source-to-site ratio for electricity is about 3.15). ENERGY STAR Portfolio Manager reports both; this calculator computes site EUI, which is what utility bills directly reflect.
How do I find my annual kWh and therm usage?
Your electricity provider's online portal or paper bills show monthly kWh consumption. Add 12 months to get the annual total. Natural gas bills show therms or CCF (hundred cubic feet): 1 CCF of natural gas is approximately 1.02 therms. Many utilities also offer a 12-month usage summary that you can request or download.
Does EUI account for climate zone?
The raw EUI figure does not adjust for climate. ENERGY STAR Portfolio Manager applies weather normalization (using degree-days) so buildings in Minneapolis and Miami can be compared fairly. The benchmarks in this calculator are unadjusted national medians, so buildings in extreme climates may appear less efficient than peers in mild climates even with identical equipment and operations.
What floor area should I use in the EUI calculation?
Use gross conditioned floor area - all spaces that are heated or cooled, measured from exterior walls. Exclude unconditioned spaces such as parking decks, open loading docks, and mechanical penthouses. If you are targeting ENERGY STAR, use the same floor area definition as ENERGY STAR Portfolio Manager to ensure consistent results.
Can I use kWh instead of kBtu for EUI?
The US standard is kBtu/ft²/yr. In Europe and most countries using SI units, the equivalent is kWh/m²/yr. To convert: multiply kBtu/ft²/yr by 3.15459 to get kWh/m²/yr. This calculator shows both. The kBtu/ft² metric is required for ENERGY STAR Portfolio Manager submissions in the United States.
How does EUI relate to ENERGY STAR score?
ENERGY STAR score is a percentile rank from 1 to 100 based on weather-normalized EUI compared to similar buildings nationally, with 50 meaning median and 75+ qualifying for certification. A lower EUI does not automatically produce a higher score unless the peer group is also controlled for climate, occupancy hours, and building characteristics - which is why ENERGY STAR Portfolio Manager applies normalization beyond a simple EUI comparison.