Gas Law Calculator
Solve any gas law problem instantly. Choose your calculator below.
All Gas Law Calculators
Ideal Gas Law (PV=nRT)
Solve for pressure, volume, moles, or temperature
Open Calculator →Combined Gas Law
Compare gas states when P, V, and T all change
Open Calculator →Charles's Law
Volume and temperature at constant pressure
Open Calculator →Boyle's Law
Pressure and volume at constant temperature
Open Calculator →Gay-Lussac's Law
Pressure and temperature at constant volume
Open Calculator →Dalton's Law
Partial pressures of gas mixtures
Open Calculator →Avogadro's Law
Volume and moles at constant T and P
Open Calculator →Which Gas Law Should I Use?
Use this quick reference table to find the right gas law for your problem:
| If You Know... | What's Constant | Use This Law | Formula |
|---|---|---|---|
| P, V, n, T (single state) | Nothing specific | Ideal Gas Law | PV = nRT |
| P, V, T (two states) | Nothing — all change | Combined Gas Law | P₁V₁/T₁ = P₂V₂/T₂ |
| P, V (two states) | Temperature | Boyle's Law | P₁V₁ = P₂V₂ |
| V, T (two states) | Pressure | Charles's Law | V₁/T₁ = V₂/T₂ |
| P, T (two states) | Volume | Gay-Lussac's Law | P₁/T₁ = P₂/T₂ |
| Multiple gas pressures | Temperature | Dalton's Law | P_total = ΣPᵢ |
| V, n (two states) | T and P | Avogadro's Law | V₁/n₁ = V₂/n₂ |
All Gas Law Formulas
| Law | Formula | Variables |
|---|---|---|
| Ideal Gas Law | PV = nRT | P = pressure, V = volume, n = moles, R = gas constant, T = temperature |
| Combined Gas Law | P₁V₁/T₁ = P₂V₂/T₂ | P, V, T at two different states |
| Boyle's Law | P₁V₁ = P₂V₂ | P and V at constant T |
| Charles's Law | V₁/T₁ = V₂/T₂ | V and T at constant P |
| Gay-Lussac's Law | P₁/T₁ = P₂/T₂ | P and T at constant V |
| Dalton's Law | P_total = P₁ + P₂ + P₃ + ... | Partial pressures of each gas |
| Avogadro's Law | V₁/n₁ = V₂/n₂ | V and n at constant T and P |
For a complete reference with rearranged forms and examples, see our Gas Law Formulas page.
How to Choose the Right Gas Law
Follow this decision process to pick the correct gas law for any problem:
Step 1: Are moles (n) involved?
If the problem gives you moles of gas or asks you to find moles, use the Ideal Gas Law (PV = nRT). This is the most general equation and works for any single-state gas problem.
Step 2: Is anything held constant?
- Temperature constant? Use Boyle's Law (P₁V₁ = P₂V₂)
- Pressure constant? Use Charles's Law (V₁/T₁ = V₂/T₂)
- Volume constant? Use Gay-Lussac's Law (P₁/T₁ = P₂/T₂)
Step 3: Does everything change?
When pressure, volume, and temperature all change between two states, use the Combined Gas Law (P₁V₁/T₁ = P₂V₂/T₂).
Step 4: Multiple gases?
For mixtures of gases, use Dalton's Law of Partial Pressures to find total or individual gas pressures.
Need more help? Check out our step-by-step solved examples.
Frequently Asked Questions
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The gas laws are a set of scientific laws that describe the behavior of ideal gases. They relate pressure (P), volume (V), temperature (T), and amount of gas (n) under various conditions. The main gas laws include the Ideal Gas Law (PV=nRT), Boyle's Law, Charles's Law, Gay-Lussac's Law, the Combined Gas Law, Dalton's Law, and Avogadro's Law.
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Choose based on what's constant: If temperature is constant, use Boyle's Law. If pressure is constant, use Charles's Law. If volume is constant, use Gay-Lussac's Law. If nothing is constant and you're comparing two states, use the Combined Gas Law. If you know moles and need P, V, or T, use the Ideal Gas Law (PV=nRT). For gas mixtures, use Dalton's Law.
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PV=nRT is the Ideal Gas Law equation where P is pressure, V is volume, n is the number of moles of gas, R is the universal gas constant (0.08206 L·atm/(mol·K) or 8.314 J/(mol·K)), and T is temperature in Kelvin. It relates all four gas variables in a single equation.
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The Combined Gas Law merges Boyle's, Charles's, and Gay-Lussac's laws into one formula: P₁V₁/T₁ = P₂V₂/T₂. It allows you to calculate changes in pressure, volume, and temperature between two states of a gas when the amount of gas stays constant.
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Yes. All gas law calculations require temperature in Kelvin. To convert: K = °C + 273.15 or K = (°F + 459.67) × 5/9. Using Celsius or Fahrenheit directly will give incorrect results because gas laws require an absolute temperature scale where 0 represents no thermal energy.