# Watts to Heat Calculator

URL: https://speedycalculator.com/calculators/physics/watts-to-heat/
Last updated: 2026-10-30

> The watts to heat calculator finds the heating power needed to raise the temperature of a mass of material by a given amount in a given time, or the temperature rise achieved by a heater.

## Inputs

- Find
- Material
- Specific heat c (J/(kg·K), kJ/(kg·K), J/(g·K), BTU/(lb·°F), cal/(g·°C))
- Mass m (kg, g, mg, t, lb, oz)
- Temperature rise ΔT (K, °C, °F)
- Heater power (kW, W, BTU/h)
- Time (min, s, h)

## Results

- Required power
- Temperature rise

## Formula

```
P = m·c·ΔT / t
```

## Explanation

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

FieldWhat to enterFindChoose one: Required power, Temperature riseMaterialChoose one: Water, Ice, Steam, Air …Specific heat cUnits: J/(kg·K), kJ/(kg·K), J/(g·K), BTU/(lb·°F), cal/(g·°C)Mass mUnits: kg, g, mg, t, lb, ozTemperature rise ΔTUnits: K, °C, °FHeater powerUnits: kW, W, BTU/hTimeUnits: 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)5006977506971,0006971,2506971,5006972,000697

## Worked 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.

## FAQ

**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.


## Sources

- [OpenStax – University Physics Volume 2](https://openstax.org/details/books/university-physics-volume-2)
- [The Engineering ToolBox](https://www.engineeringtoolbox.com/)