Avogadro's Law (V₁/n₁ = V₂/n₂)

At constant T, P: volume scales with number of moles.

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How to use this calculator

  • Enter V₁, n₁, n₂.
  • Read V₂.

About this calculator

Avogadro's Law (1811): at the same T and P, equal volumes of any gas contain equal numbers of molecules. 22.414 L at STP = 1 mole = 6.022 × 10²³ molecules. Doubling moles doubles volume. Foundation of stoichiometry — the same gas-volume ratio works regardless of identity. Avogadro's number 6.022 × 10²³ is now defined exactly (post-2019 SI redefinition).

Frequently asked

STP volume?+
22.414 L per mole at 273.15 K and 101.325 kPa.
Avogadro's number?+
6.02214076 × 10²³ molecules/mol. Defined exactly since 2019 SI redefinition.
Same for all gases?+
Yes — at given T, P, equal moles = equal volume. (Ideal gas assumption.)
Why "mole" word?+
From "molecule" — Wilhelm Ostwald coined it 1893. Latin "moles" = pile/heap.
Real gas deviation?+
Avogadro held best at low pressure. Near condensation: molecules attract, taking less volume than predicted.

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