Convert Calorie to Watt-Hour (cal → Wh)

Converting calories to watt-hours is straightforward: multiply by the conversion factor. Follow these three steps to do it by hand or in your head.

1. 1
   Take your value in calories

   Start with the number of calories (cal) you want to convert.
2. 2
   Multiply by 0.001162

   The conversion factor from cal to Wh is 0.001162. Multiply your value by this number.
3. 3
   Read the result in watt-hours

   The result is your value in watt-hours (Wh).

Multiply the value in calories by 0.001162. For the reverse direction, multiply by 860.42065.

• ✓1 cal = 4.184 J. 1 kcal = 4184 J.
• ✓Scientific "calorie" and nutrition "Calorie" differ by 1000×.
• ✓Prefer joules in modern scientific writing.

• ✗Assuming "calories" on food labels means gram calories — they are kcal.
• ✗Mixing gram calories and kilocalories in calculations.
• ✗Confusing calorie (energy) with calorimeter (apparatus).

What is the Calorie?

The calorie equals exactly 4.184 joules (the 'thermochemical calorie') and is the historical unit for heat in chemistry and physics. It was originally defined as the heat needed to raise 1 gram of water by 1°C (a definition that varied slightly with starting temperature, hence multiple 'calories' — 4.184 J was set as the exact thermochemical convention). The calorie is widely used in older physics and chemistry literature for reaction energies, specific heat capacities, and thermodynamic calculations. Note: this 'small calorie' (lowercase c) is 1/1000 of the food Calorie (capital C) used in nutrition. The chemistry calorie relates to the joule (4.184 J = 1 cal), the kilocalorie (1,000 cal = 1 kcal = 1 food Calorie), and the BTU (1 BTU ≈ 252 cal). Modern SI usage in scientific publications has largely replaced the calorie with the joule, but it persists in medical and chemistry contexts.

• Thermodynamics and older physics texts
• Chemistry energy calculations
• Some engineering heat-transfer contexts

What is the Watt-Hour?

The watt-hour equals exactly 3,600 joules and is the standard unit for small-battery capacity, household electrical energy, and renewable-energy storage. A smartphone battery stores roughly 12–15 Wh, a laptop battery 50–100 Wh, and an electric car battery 60,000–100,000 Wh (60–100 kWh). The watt-hour represents the energy delivered by a 1-watt device running for 1 hour. It is the natural unit for connecting power (watts) to time, which is why electric utilities bill in kilowatt-hours. The watt-hour relates to the joule (3,600 J = 1 Wh), the kilowatt-hour (1,000 Wh = 1 kWh), and the BTU (1 Wh ≈ 3.412 BTU). Battery capacity, solar panel output (Wh per day), and energy storage system specifications all rely on the watt-hour as the base small-energy unit.

• Laptop and phone battery capacity
• Portable power banks and UPS
• Home solar panel daily output