Boiling Point and Altitude

Features

• Three modes: altitude to boiling point, boiling point to altitude, pressure to boiling point
• ⚠️ Pressure from the International Standard Atmosphere (ISA), not linear interpolation
• ⚠️ Boiling point from a Clausius–Clapeyron approximation with consistent, sourced constants
• ⚠️ Anchors pinned: altitude 0 → 100.00 °C, and 3,000 m ≈ 89.9 °C
• Gives the pressure, temperature and boiling point at that place
• Cooking-time correction (noodles / rice / sterilisation) as an empirical range
• ⚠️ Notes that sterilising at altitude needs a pressure canner, not just more time
• Computed locally with no network requests

How to use

1. Pick a mode (from altitude, from boiling point, or from pressure)
2. Enter the matching value (metres, degrees Celsius, or kPa)
3. Optionally pick a cooking-time correction (none / noodles / rice / sterilisation)
4. The right-hand side gives altitude, pressure, boiling point and how much longer to cook

FAQ

At what temperature does water boil at 3,000 m?

About 89.9 °C. Under the Standard Atmosphere the pressure at 3,000 m is roughly 70.1 kPa, and the Clausius–Clapeyron approximation gives 89.9 °C. Note that you cannot linearly interpolate between the 100 °C at sea level and some higher point: pressure falls exponentially with altitude, so a straight line is more than 1 °C out at 3,000 m. This is the tool’s default example — open it and check.

Why does cooking take longer at altitude?

Because the boiling point drops. Most cooking reactions speed up with temperature, and when water boils at 90 °C rather than 100 °C the food cannot reach 100 °C internally, so reactions and starch gelatinisation slow down. Empirically the time rises by tens of percent, more so the higher you are. The tool gives a range based on “a few percent longer per degree the boiling point falls” — it varies with the food, the pan and the stove, so it was never a precise value.

How do you sterilise water at altitude?

Time alone is not enough. Boiling does kill bacteria and viruses, but at 90 °C water cannot reliably kill certain spores (such as botulinum), so canning and similar tasks needing a higher temperature call for a pressure canner, which raises the boiling point back above 100 °C. The “sterilisation” correction here only gives the empirical time range and flags this point — time cannot solve a temperature ceiling.