How powerful must a heater be to warm a tank, a room’s air or a piece of metal in a set time? Divide the energy needed by the time available. In reverse, the same relation tells how fast a known heater warms something.
How to use the Watts to Heat Calculator
- Find
- Material
- Specific heat c
- Mass m
- Temperature rise ΔT
- Heater power
- Time
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Choose what to find, the material, and enter the values.
Tips
- Use absolute temperature (K) in gas laws and efficiency formulas.
- Temperature differences are the same in K and °C.
- Heat = mass × specific heat × temperature change when no phase change occurs.
- Phase changes need latent heat at a constant temperature.
Common mistakes to avoid
- Using °C in pV = nRT.
- Forgetting latent heat during melting or boiling.
- Confusing heat capacity (J/K) with specific heat (J/(kg·K)).
Inputs explained
| Field | What to enter |
|---|---|
| Find | Choose one: Required power, Temperature rise |
| Material | Choose one: Water, Ice, Steam, Air … |
| Specific heat c | Units: J/(kg·K), kJ/(kg·K), J/(g·K), BTU/(lb·°F), cal/(g·°C) |
| Mass m | Units: kg, g, mg, t, lb, oz |
| Temperature rise ΔT | Units: K, °C, °F |
| Heater power | Units: kW, W, BTU/h |
| Time | Units: min, s, h |
Example values
How the main result changes when Specific heat c changes and everything else stays at the example values above:
| Specific heat c (J/(kg·K)) | Required power (W) |
|---|---|
| 500 | 697 |
| 750 | 697 |
| 1,000 | 697 |
| 1,250 | 697 |
| 1,500 | 697 |
| 2,000 | 697 |
Formula
P = m·c·ΔT / tWorked example
Inputs — Find: Required power; Material: Water; Mass m: 10 kg; Temperature rise ΔT: 30 K; Time: 30 min.
Results — Required power = 697 W.
Key terms
- Heating power
- Energy delivered per unit time.
Frequently asked questions
How much power heats 10 L of water by 30 °C in 30 minutes?
About 700 W (without losses).
Should I add a margin?
Yes – heat losses can be significant.
How many BTU/h is 1 kW?
About 3,412 BTU/h.
Does this include phase changes?
No – melting or boiling needs extra latent heat.
What formula does the Watts to Heat Calculator use?
P = m·c·ΔT / t.