How do you calculate the new volume or temperature?

Rearrange V₁/T₁ = V₂/T₂ for the unknown. New volume is V₂ = V₁ × T₂ / T₁; new temperature is T₂ = T₁ × V₂ / V₁. For example 2 litres at 300 K heated to 600 K gives V₂ = 2 × 600 / 300 = 4 litres. The temperatures must be in kelvin, but the volume can be in any unit because it cancels — the answer comes out in whatever volume unit you supplied.

What happens to gas volume when you heat it?

At constant pressure the volume increases in direct proportion to the absolute temperature. Warm a gas from 300 K to 330 K — a 10% rise in kelvin — and its volume grows by 10%. The molecules move faster and push the container walls out until the pressure rebalances, so the gas occupies more space. This is the principle behind hot-air balloons: heated air expands, becomes less dense, and lifts.

Does pressure stay constant in Charles's Law?

Yes. Charles's Law applies only when pressure and the amount of gas are held constant — it is the isobaric case. If the pressure changes as well, you need the combined gas law (P₁V₁/T₁ = P₂V₂/T₂) or the full ideal gas law PV = nRT. So the calculator assumes the gas can expand or contract freely against a fixed external pressure, like air in a flexible balloon.

Charles's Law Calculator — V₁/T₁ = V₂/T₂

Temperature	Volume	Note
300 K (27 °C)	2 L	start
450 K	3 L	×1.5
600 K	4 L	double temp

Charles's Law describes how a fixed amount of gas behaves when you change its temperature at constant pressure: the volume is directly proportional to the absolute temperature, so V₁/T₁ = V₂/T₂. Heat the gas and it expands; cool it and it contracts — in exact proportion to the temperature measured in kelvin. The one rule that trips people up is that temperature must be absolute: a gas at 600 K really does occupy twice the volume it has at 300 K, but 600 °C and 300 °C are not in a 2:1 ratio at all.

Reviewed: June 19, 2026 · Author: Naveen P N, Founder — AI Calculator · Verified against: Charles's Law as the isobaric case of PV = nRT.

The Charles's Law equations

Charles's Law

V₁ / T₁ = V₂ / T₂ (T in kelvin)

Final volume

V₂ = V₁ × T₂ / T₁

Kelvin conversion

T(K) = T(°C) + 273.15

The ratio of volume to absolute temperature is a constant for the gas while pressure and amount stay fixed. To find any one quantity, set the two ratios equal and cross-multiply. Volume units cancel, so litres or millilitres both work, but the temperatures must be in kelvin — the proportionality is to absolute temperature, measured from absolute zero, not from the freezing point of water.

Worked example — heating a gas

Scenario: A 2-litre sample of gas at 300 K (27 °C) is heated to 600 K at constant pressure. What is the new volume?

Final volume

V₂ = 2 L × 600 K / 300 K = 4 L

Check the ratio

2 / 300 = 0.00667 = 4 / 600 ✓

Doubling the absolute temperature doubles the volume to 4 litres — the ratio V/T stays at 0.00667 L/K throughout. Heat the same gas to only 450 K and it would expand to 3 litres (a factor of 1.5, matching 450/300). Note that if you had wrongly used Celsius — 27 °C to 327 °C — you would get a completely different and incorrect answer, which is why the kelvin scale is essential here.

Related chemical calculators

Boyle's Law Calculator — P₁V₁ = P₂V₂.
Ideal Gas Law Calculator — PV = nRT.
Moles Calculator — n = m/M.
Molarity Calculator — moles per litre.
Specific Gravity Calculator — relative density.

Frequently Asked Questions

What is Charles's Law?⌄

At constant pressure, gas volume is directly proportional to absolute temperature: V₁/T₁ = V₂/T₂. Double the kelvin, double the volume.

How do I find the new volume?⌄

V₂ = V₁·T₂/T₁. e.g. 2 L × 600 K ÷ 300 K = 4 L. New temp is T₂ = T₁·V₂/V₁.

Why must temperature be in kelvin?⌄

The law uses absolute temperature from absolute zero. Add 273.15 to °C. Celsius gives wrong, even negative, volumes.

What happens when you heat a gas?⌄

It expands in proportion to kelvin. 300 K → 330 K (+10%) grows volume by 10%. Basis of hot-air balloons.

Does pressure stay constant?⌄

Yes — it's the isobaric case. If P changes too, use P₁V₁/T₁ = P₂V₂/T₂ or PV = nRT.

Charles's Law Calculator

Charles's Law — Quick answer