Boiling Point vs Altitude

As altitude increases, atmospheric pressure decreases, so water does not need to get as hot before its vapor pressure matches the air pressure and it starts to boil. This formula gives a quick estimate of how many degrees Celsius the boiling point drops for each metre of elevation gain. It is a practical approximation, not an exact physical law, so it works best for everyday cooking and moderate altitudes.

Use this when adjusting cooking times or temperatures in places above sea level, such as mountain towns, hiking shelters, or high-altitude baking. It is also helpful for science problems that need an estimated boiling point from elevation.

• Using kilometres instead of metres for h
• Adding the altitude instead of subtracting its effect from 100°C
• Treating the result as exact rather than an approximation