Energy Converter
Convert energy with the joule as the SI base unit.
Enter Energy and Units
Table of Contents
Complete Guide to Energy Units
Energy describes the capacity to do work or transfer heat. The SI unit is the joule (J). Nutrition labels often use kilocalories (kcal), electricity bills use kilowatt-hours (kWh), and HVAC equipment in the US may quote BTU.
Common energy units
| Unit | Typical use | ≈ joules |
|---|---|---|
| 1 kJ | Mechanical work, chemistry | 1000 |
| 1 kcal | Food energy | 4184 |
| 1 Wh | Small battery capacity | 3600 |
| 1 kWh | Utility metering | 3.6e6 |
Calorie definitions
The thermochemical calorie used here is 4.184 J. Some fields use a slightly different calorie; always check regulatory context for food labeling.
Power (watts) times time (seconds) gives energy in joules. kWh is kilowatts times hours, not a rate.
Frequently asked questions
- What is a joule in everyday terms?
- Roughly the energy to lift a small apple one meter, or the heat to warm a gram of water by about a quarter of a degree Celsius.
- Are food Calories the same as calories here?
- Food labels often mean kilocalories when they write Cal with a capital C. This converter uses kcal explicitly.
- How does kWh relate to my bill?
- Utilities charge per kWh consumed. Multiplying kWh by your tariff rate gives cost; this tool only converts units.
- Is BTU still used?
- Yes for heating and cooling equipment ratings in the United States, especially furnaces and air conditioners.
- What is a watt-hour?
- One Wh is the energy delivered by one watt running for one hour (3600 J). Phone batteries are often labeled in Wh or mWh.
Energy Conversion Formulas
Each unit maps to joules with a fixed factor. Multiply by factor(from) to get J, then divide by factor(to).
Example: 1 kWh = 3,600,000 J = 3600 kJ ≈ 860 kcal (thermochemical).
Pro Tip:
On electricity labels, multiply watts by hours of use to estimate kWh before converting to BTU or MJ for comparison with gas appliances.
How to Convert Energy
Enter the energy amount, choose From and To units, then submit. For manual checks, convert to joules first.
-
1Enter the energy value from a label, meter or calculation.
-
2Select energy units (J, kJ, kcal, kWh, BTU, etc.).
-
3Click Convert Energy to see the result.
-
4Cross-check with a known reference (1 kWh = 3.6 MJ) if the reading seems wrong.
Quick sanity check:
Food labels may list kJ and kcal side by side. Utility bills show kWh; battery packs sometimes list Wh.
Common Use Cases
Pick the output unit that matches your domain: nutrition, electricity, or mechanical work.
Nutrition
Compare kcal on packaging with kJ where regulations require dual labeling.
Electricity
Convert appliance kWh ratings to MJ or BTU for cross-border spec sheets.
Mechanical work
Lift energy and impact tests often report joules or foot-pounds; this tool covers SI and common US thermal units.
HVAC
Heating and cooling capacity may be quoted in BTU/h (a power) while this converter handles energy amounts in BTU.
Do not confuse energy (J, kWh) with power (W, kW).
Practical Examples
Worked conversions using the same joule factors as this calculator.
Example 11000 J to kJ
1000 / 1000 = 1 kJ
Example 21 kWh to MJ
1 × 3.6e6 / 1e6 = 3.6 MJ
Example 32000 kcal to kJ
2000 × 4184 / 1000 = 8368 kJ
Example 410000 BTU to kWh
10000 × 1055.056 / 3.6e6 ≈ 2.93 kWh