Energy units: watt-hours, kilowatt-hours and Btu.
How do energy units differ from watts without implying an equipment-sizing result?
A kilowatt is not a kilowatt-hour
EIA defines watt-hours as energy from power used over time and kilowatt-hours as the corresponding thousand-watt-hour unit. A 1 kW power figure does not tell you an energy total without a duration or a measured consumption record.
State the constant-power assumption
The 100 W for three hours example assumes that power remains constant for the stated interval. Equipment that cycles, changes mode or has a different measured input needs an appropriate measured record. The arithmetic is not a load, efficiency or heating-capacity assessment.
Label a rounded Btu conversion
EIA’s published comparison table uses the rounded factor 1 kWh = 3,412 Btu. Preserve that stated basis rather than presenting all derived decimals as exact. A fuel volume requires its own supplied energy-content basis; an electrical energy conversion does not infer fuel use or system efficiency.
Use the right available reference
The site’s existing Unit Converter covers its displayed length, area, volume, mass, liquid and coverage units; it does not currently offer this energy-unit conversion. Use the cited EIA reference for energy conversions rather than forcing an energy value into an unrelated calculator. No new equipment-sizing tool is implied.
Use this decision sequence
- Identify whether the given figure describes power or energy.
- Keep the supplied duration visible when multiplying power by time.
- Convert Wh to kWh by dividing by 1,000.
- Use the stated Btu conversion basis and label its precision.
Keep the quantities distinct
| Quantity or assumption | How to use it |
|---|---|
| Watts | Power, not accumulated energy. |
| Watt-hours | Power multiplied by a supplied duration. |
| Kilowatt-hours | 1,000 Wh per kWh. |
| Btu | A heat-energy unit; keep the conversion basis visible. |
Worked comparison
A supplied constant 100 W scenario lasting 3 h uses 300 Wh, or 0.3 kWh. Using EIA’s rounded reference factor of 3,412 Btu per kWh gives 1,023.6 Btu.
Check before using the estimate
Rated power and duration do not necessarily describe the actual operating energy of an appliance.
All dimensions, product properties, prices and specifications in this example are illustrative arithmetic inputs. Use the values from your measured plan, selected product data sheet and supplier quote. This guide does not choose construction specifications or certify safety.
Sources and product references
References support the factual distinctions and scope described above. Growing guidance is regional and care instructions are product-specific. Worked numerical examples are independent illustrative arithmetic.
Calculation and scope checked 2026-10-13. Methods and scope.