Avogadro's Law Calculator
Find gas volume change with amount of gas.
Results update as you type.
How it works
Avogadro's law describes how the volume of a gas changes as you add or remove gas at constant temperature and pressure, and this calculator finds the resulting volume. You enter the initial volume, the initial number of moles, and the final number of moles, and it returns the new volume. The law states that volume is directly proportional to the amount of gas in moles: double the moles and the volume doubles, halve them and it halves, as long as temperature and pressure stay fixed. This reflects the deeper insight, credited to Amedeo Avogadro, that equal volumes of any gas at the same temperature and pressure contain the same number of molecules, regardless of the gas. It is one of the fundamental gas laws and, combined with Boyle's and Charles's laws, builds up to the ideal gas law. A familiar illustration is inflating a balloon: as you add gas, the balloon expands in proportion. It also underlies the concept of molar volume, the fixed volume one mole of any ideal gas occupies at a given temperature and pressure. The units of volume can be anything as long as they are consistent, since the calculation uses the ratio of moles. Chemistry students and scientists use it to relate gas quantities and volumes. Enter the initial volume and moles and the final moles to compute the final volume.
V₁/n₁ = V₂/n₂ → V₂ = V₁ × n₂ / n₁
Avogadro's law states that at constant temperature and pressure, the volume of a gas is directly proportional to the number of moles present. So the initial volume divided by initial moles equals the final volume divided by final moles. The final volume equals the initial volume times the ratio of final to initial moles. More gas means proportionally more volume.
Source:Chemistry (gas laws)
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Worked example
How to use this calculator
- 1
Enter your values
Enter initial volume (v₁), initial moles (n₁) and final moles (n₂).
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Final volume (V₂) updates instantly as you type — no button to press.
Frequently asked questions
What is Avogadro's law?
Avogadro's law states that at constant temperature and pressure, the volume of a gas is directly proportional to the number of moles of gas. Adding more gas increases the volume proportionally, and removing gas decreases it. It reflects that equal volumes of gases at the same conditions hold equal numbers of molecules.
How do you calculate volume with Avogadro's law?
Multiply the initial volume by the ratio of final moles to initial moles. So the final volume equals initial volume times final moles divided by initial moles. Enter the three known values and the calculator returns the new volume, keeping temperature and pressure constant as the law requires.
What conditions must stay constant?
Avogadro's law holds only when temperature and pressure remain constant while the amount of gas changes. If temperature or pressure also change, you need Charles's law, Gay-Lussac's law, or the full ideal gas law instead. Avogadro's law is the special case that isolates the effect of the amount of gas on volume.
What is molar volume?
Molar volume is the volume that one mole of an ideal gas occupies at a specified temperature and pressure. At standard temperature and pressure it is about 22.4 liters per mole. Avogadro's law underlies this idea, since equal moles of any gas take the same volume under identical conditions, giving a universal molar volume.
What is a real-world example of Avogadro's law?
Inflating a balloon or tire demonstrates it: as you pump in more gas, adding moles, the volume increases in proportion at roughly constant temperature and pressure. Breathing also reflects it, as expanding the lungs draws in more air. Any situation where adding gas expands a flexible container illustrates Avogadro's law.