What are all the gas law formulas?

The main gas law formulas are: PV=nRT (Ideal), P₁V₁/T₁=P₂V₂/T₂ (Combined), P₁V₁=P₂V₂ (Boyle's), V₁/T₁=V₂/T₂ (Charles's), P₁/T₁=P₂/T₂ (Gay-Lussac's), P_total=ΣPᵢ (Dalton's), and V₁/n₁=V₂/n₂ (Avogadro's).

Which gas law formula should I use?

If moles are involved, use Ideal Gas Law. If temperature is constant, use Boyle's. If pressure is constant, use Charles's. If volume is constant, use Gay-Lussac's. If everything changes, use Combined. For gas mixtures, use Dalton's.

Do all gas law formulas require Kelvin?

Yes, any gas law formula involving temperature requires absolute temperature in Kelvin. Convert from °C by adding 273.15, or from °F using K = (°F + 459.67) × 5/9.

How are the gas laws related?

All the individual gas laws (Boyle's, Charles's, Gay-Lussac's) are special cases of the Combined Gas Law. The Ideal Gas Law is the most general form that also accounts for the amount of gas (moles).

Gas Law Formulas: Complete Reference

All seven gas law formulas in one place. Use this reference chart to find the right formula for any gas law problem.

Master Gas Law Formula Table

Law	Formula	What's Constant	When to Use
Ideal Gas Law	PV = nRT	—	Single-state problems with moles
Combined Gas Law	P₁V₁/T₁ = P₂V₂/T₂	n (moles)	Two-state problems, all variables change
Boyle's Law	P₁V₁ = P₂V₂	T, n	Pressure-volume at constant temperature
Charles's Law	V₁/T₁ = V₂/T₂	P, n	Volume-temperature at constant pressure
Gay-Lussac's Law	P₁/T₁ = P₂/T₂	V, n	Pressure-temperature at constant volume
Dalton's Law	P_total = P₁ + P₂ + ...	T	Gas mixtures, partial pressures
Avogadro's Law	V₁/n₁ = V₂/n₂	T, P	Volume-moles at constant T and P

Each Law Explained

Ideal Gas Law (PV = nRT)

The most general gas law. It relates pressure, volume, moles, and temperature at a single state. The gas constant R must match your chosen units. Use the calculator →

Combined Gas Law (P₁V₁/T₁ = P₂V₂/T₂)

The Combined Gas Law merges Boyle's, Charles's, and Gay-Lussac's laws into one equation. It compares a gas at two different states when the amount of gas remains constant. If any single variable stays constant, the equation simplifies to one of the simpler laws below. Use the combined law when pressure, volume, and temperature all change simultaneously. Use the calculator →

Boyle's Law (P₁V₁ = P₂V₂)

Boyle's Law describes the inverse relationship between pressure and volume at constant temperature. When you compress a gas (decrease volume), its pressure increases proportionally. When you expand a gas (increase volume), the pressure drops. Doubling the pressure cuts the volume in half. This law applies to processes like syringes, scuba diving, and vacuum pumps. Use the calculator →

Charles's Law (V₁/T₁ = V₂/T₂)

Charles's Law shows a direct proportional relationship between volume and absolute temperature at constant pressure. When you heat a gas, it expands; when you cool it, the volume shrinks. Temperature must always be measured in Kelvin for this law to work correctly. Practical examples include hot air balloons rising when heated and balloons shrinking in cold weather. Use the calculator →

Gay-Lussac's Law (P₁/T₁ = P₂/T₂)

Gay-Lussac's Law relates pressure and temperature at constant volume. When a gas is heated in a rigid, sealed container, its pressure rises in direct proportion to the temperature increase. This explains why aerosol cans carry warnings about heat exposure and why tire pressure increases on hot days. Use the calculator →

Dalton's Law (P_total = ΣPᵢ)

Dalton's Law of Partial Pressures states that the total pressure of a gas mixture equals the sum of each individual gas's partial pressure. Each gas in a mixture exerts pressure independently as if the other gases were not present. Partial pressures can also be calculated using mole fractions: Pᵢ = Xᵢ × P_total. This law is essential in scuba diving, anesthesiology, and atmospheric science. Use the calculator →

Avogadro's Law (V₁/n₁ = V₂/n₂)

Avogadro's Law states that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules. Volume is directly proportional to the number of moles when temperature and pressure are constant. At STP (0°C, 1 atm), one mole of any ideal gas occupies exactly 22.4 liters, known as the molar volume. Use the calculator →

How to Choose the Right Gas Law

Selecting the correct gas law depends on two questions: what variables are involved, and what is held constant? Follow this decision process:

Are moles (n) involved? → Use the Ideal Gas Law (PV = nRT). This is the most versatile equation and works whenever you know or need to find the number of moles.
Is temperature constant? → Use Boyle's Law (P₁V₁ = P₂V₂). The problem will typically say "at constant temperature" or "isothermal."
Is pressure constant? → Use Charles's Law (V₁/T₁ = V₂/T₂). Look for phrases like "at constant pressure" or "isobaric."
Is volume constant? → Use Gay-Lussac's Law (P₁/T₁ = P₂/T₂). Clue words include "rigid container," "sealed tank," or "constant volume."
Nothing constant? → Use the Combined Gas Law (P₁V₁/T₁ = P₂V₂/T₂). This handles all three variables changing at once.
Multiple gases mixed together? → Use Dalton's Law (P_total = ΣPᵢ).

For worked problems demonstrating each law, see our solved examples page. For help with units and the gas constant, see PV=nRT Units and Gas Constant R Values.

Frequently Asked Questions

The main gas law formulas are: PV=nRT (Ideal), P₁V₁/T₁=P₂V₂/T₂ (Combined), P₁V₁=P₂V₂ (Boyle's), V₁/T₁=V₂/T₂ (Charles's), P₁/T₁=P₂/T₂ (Gay-Lussac's), P_total=ΣPᵢ (Dalton's), and V₁/n₁=V₂/n₂ (Avogadro's).
If moles are involved, use Ideal Gas Law. If temperature is constant, use Boyle's. If pressure is constant, use Charles's. If volume is constant, use Gay-Lussac's. If everything changes, use Combined. For gas mixtures, use Dalton's.
Yes, any gas law formula involving temperature requires absolute temperature in Kelvin. Convert from °C by adding 273.15, or from °F using K = (°F + 459.67) × 5/9.
All the individual gas laws (Boyle's, Charles's, Gay-Lussac's) are special cases of the Combined Gas Law. The Ideal Gas Law is the most general form that also accounts for the amount of gas (moles).