Water boils cooler at altitude. This tool tells you how much cooler, and what to aim for at the kettle.
This tool estimates standard atmospheric pressure from elevation, then estimates the saturation temperature of water with an Antoine vapour-pressure approximation. It replaces the earlier linear altitude rule. It supports −500 to 8,000 metres (or the equivalent in feet); weather and local pressure are not measured.
Check: sea level is about 100°C, 1,000 metres about 96.7°C, and 5,000 metres about 83.3°C. The suggested kettle starting point is the lower of 96°C and one degree below the calculated boiling point, so it never asks an open kettle to exceed its own boiling limit.
This is a brewing estimate, not a pressure-boiler or food-processing specification. The empirical vapour-pressure fit is approximate, particularly near its temperature limits. For background see NASA’s atmosphere model and NIST’s explanation of Antoine equations. Coefficients and units are documented in the calculation module.
Espresso machines pressurise the boiler above ambient pressure, so altitude has a smaller effect. This tool is aimed at kettle-based brewing.
No. This is a standard-atmosphere and vapour-pressure estimate; weather and measurement errors are not included. Use a thermometer if you need the actual temperature.
Extraction is temperature-dependent. Cooler water dissolves fewer flavor compounds, so under-extraction (sour, weak) becomes more likely at altitude.
Yes. Every degree matters. Pre-warm your brewer and mug with hot water before brewing.