Understanding Boyle's Law
Boyle's Law describes how a gas behaves when you change its pressure or volume while keeping its temperature and the amount of gas fixed. Discovered by Robert Boyle in 1662, it says that pressure and volume move in opposite directions: squeeze a gas into a smaller space and its pressure rises; let it expand and its pressure falls. The relationship is precise, not just directional — the product of pressure and volume stays constant.
The formula
Boyle's Law is written P1V1 = P2V2, where P1 and V1 are the initial pressure and volume, and P2 and V2 are the pressure and volume after the change. Because the product PV is constant (call it k), any one unknown can be found once the other three values are known:
- Solving for final volume: V2 = (P1 × V1) / P2
- Solving for final pressure: P2 = (P1 × V1) / V2
- Boyle's constant: k = P1 × V1 = P2 × V2, which stays fixed for that sample of gas at that temperature
This calculator takes your initial pressure, initial volume, and final pressure, then solves for the final volume — the most common version of the problem in chemistry and physics courses.
Working with units
- Pressure must be absolute pressure, not gauge pressure — a tire gauge reading 0 psi is actually at roughly 1 atm absolute, since it measures pressure above atmospheric.
- Use consistent units on each side of the equation: if P1 and P2 are both in atmospheres, the result is unaffected by switching the pair to kPa or mmHg, as long as both pressures use the same unit.
- The same logic applies to volume — liters, milliliters, or cubic meters all work as long as V1 and V2 (or the V2 you're solving for) share one unit.
Limits of Boyle's Law
Boyle's Law assumes an ideal gas: a fixed amount of gas, constant temperature (an isothermal process), and no phase change. It closely matches real gases — air, helium, nitrogen — at everyday pressures and temperatures. It breaks down at very high pressure or very low temperature, where intermolecular attractions and the physical volume of gas molecules become significant, and near the point where the gas would condense into a liquid.
Frequently Asked Questions
What is Boyle's Law?
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| Category | % of Net Income | Examples |
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Common Measurement Conversions for Everyday Use
| Quantity | US / Imperial | Metric Equivalent |
|---|---|---|
| 1 cup | 8 fl oz | 237 mL |
| 1 pint | 16 fl oz | 473 mL |
| 1 quart | 32 fl oz | 946 mL |
| 1 gallon | 128 fl oz | 3.785 L |
| 1 lb | 16 oz | 453.6 g |
| 1 ft | 12 in | 30.48 cm |