Candy Making Altitude Calculator
Lower a candy recipe’s finish temperature for your altitude by how much lower water boils there, from your elevation, a barometer or your own thermometer.
Result
Enter finish temperature in the recipe to see the result.
https://calcgallery.com/baking/candy-altitude-calculator/
Results are arithmetic on the figures you enter. Cooking times are estimates: ovens, cuts and starting temperatures vary, so check doneness with a thermometer. Safe temperatures are the USDA's; guidance differs by country, so check your own. Read the full disclaimer
How to use the Candy Making Altitude Calculator
- Enter the finish temperature your recipe gives, such as the soft-ball or hard-crack temperature.
- Choose how to find the boiling point of water where you are, then enter your altitude, the temperature your water boils at, or a barometer reading.
- Cook the syrup to the temperature shown, not the one in the recipe.
The rule
A sugar syrup’s stages, from thread and soft ball to hard crack, correspond to how concentrated the syrup is, and a thermometer tracks concentration by how far the syrup’s boiling point has risen above water’s. At altitude, water boils lower, so every stage arrives at a lower temperature by the same amount. Colorado State University Extension puts it as a subtraction:
cook to = recipe temperature − (212 °F − the temperature water boils at here)Three ways to find the boiling point
- Measured. Boil water and read your candy thermometer. This is the extension service’s own method, and it corrects for the day’s weather and your thermometer at once. The drop is the difference from 212 °F, the boiling point a sea-level recipe is written for.
- From altitude. The page works out the standard-atmosphere air pressure for your altitude and the temperature water boils at under it, with the same method as the boiling point at altitude page, and subtracts that from its sea-level boiling point.
- From a barometer. Enter the absolute air pressure where you are, not the sea-level-adjusted figure a weather report gives.
From an altitude, the page also shows the extension service’s rule of thumb of 2 °F per 1,000 feet for comparison.
What the page leaves out
Humidity also affects candy, particularly on how it sets and keeps. It is not modelled. Cold-water tests, dropping a little syrup into cold water and checking its firmness, work at any altitude and are a useful check on the thermometer.
With your numbers
- Water boils at 202.4 °F here, 9.6 °F below its sea-level boiling point
- Cook to = 240 °F − 9.6 °F = 230 °F
Quick reference
Weather moves the boiling point a degree or so. Testing your thermometer in boiling water on the day is the most direct check.
| Example | Cook to |
|---|---|
| Soft ball, 240 °F, at 5,280 ft | 230 °F |
| Firm ball, 245 °F, at 7,000 ft | 232 °F |
| Hard crack, 300 °F, at 8,000 ft | 285 °F |
| Fudge, 235 °F, at 3,000 ft | 230 °F |
| 240 °F with water boiling at 202 °F | 230 °F |
| 115 °C at 1,600 m | 110 °C |
| 150 °C at 2,500 m | 142 °C |
| 120 °C with a barometer reading of 84 kPa | 115 °C |
Where the numbers come from
The fixed figures this calculator relies on, and the published source each one was checked against. How the calculators are built and checked
8 sources
U.S. Standard Atmosphere, 1976 (NOAA-S/T 76-1562), Table 2, P₀ = 1.013250 × 10^5 N/m² (or Pa). https://www.ngdc.noaa.gov/stp/space-weather/online-publications/miscellaneous/us-standard-atmosphere-1976/us-standard-atmosphere_st76-1562_noaa.pdf
Used for
- Standard sea-level atmospheric pressure P₀ of the standard atmosphere.
U.S. Standard Atmosphere, 1976, Table 2 and p. 4: T₀ = 288.15 K.
Used for
- Standard sea-level temperature T₀, 15 °C.
U.S. Standard Atmosphere, 1976, Table 4: L(M,0) = −6.5 K/km′ from H₀ = 0 to H₁ = 11 km′.
Used for
- The fall in temperature with height in the lowest layer of the standard atmosphere, 0 to 11 geopotential kilometres.
U.S. Standard Atmosphere, 1976, p. 9, section 1.2.4: M₀ = 28.9644 kg/kmol.
Used for
- Mean molar mass of sea-level dry air M₀ in the standard atmosphere.
U.S. Standard Atmosphere, 1976, Table 2 and p. 3: R* = 8.31432 × 10^3 N·m/(kmol·K).
Used for
- The gas constant R* the standard atmosphere is defined with. Not the 2019 SI value; the Standard says it is not exactly consistent with k and N_A.
U.S. Standard Atmosphere, 1976, Table 2 and p. 3: g₀ = 9.80665 m/s².
Used for
- Standard acceleration of gravity g₀, the value adopted by the CIPM in 1901.
U.S. Standard Atmosphere, 1976, Table 2 and p. 4: r₀ = 6356.766 km.
Used for
- Effective earth radius r₀ used to convert geometric altitude to geopotential altitude.
Colorado State University Extension, High Altitude Food Preparation (undated PDF), "Candy, Syrup and Jelly Making": "first test the temperature at which your water boils, then reduce the finish temperature by the difference between the temperature of your boiling water and 212 degrees. This is an approximate decrease of 2 degrees for every increase of 1,000 feet", https://www.extension.colostate.edu/wp-content/uploads/2021/11/High-Altitude-PDFv3.pdf; and FoodSmart Colorado, Candy Making at High Elevation (reviewed October 2025), https://extension.colostate.edu/resource/candy-making-at-high-elevation/: "For each 1,000 feet above sea level, reduce the temperatures in the recipe by 2°F."
Used for
- The extension rule of thumb for candy at elevation: lower the finish temperature 2 °F for every 1,000 ft above sea level. Stored as kelvin per metre.
Common questions about the Candy Making Altitude Calculator
- How do I adjust candy temperatures for high altitude?
- Lower the recipe’s finish temperature by however many degrees below 212 °F water boils where you are. Colorado State University Extension gives this rule: test the temperature at which your water boils, then reduce the finish temperature by the difference. The page does the subtraction, and can estimate the boiling point from your altitude if you do not want to test it.
- Why do candy temperatures change with altitude?
- Air pressure is lower at altitude, so water boils at a lower temperature. A sugar syrup boils at a temperature set by how much water is left in it, and at altitude every stage is reached at a lower temperature. Cooking to the sea-level number boils off too much water, which gives candy that is harder and grainier than intended.
- What is the 2 °F per 1,000 feet rule?
- It is the extension service’s approximation of the same drop: about 2 °F lower for every 1,000 feet above sea level. When you work from an altitude, the page shows it beside the answer from the boiling point, and the rule of thumb comes out a little lower, by more the higher you go.
- Is measuring my water’s boiling point better than using my altitude?
- It can be. Weather moves the air pressure, and with it the boiling point, by a degree or so from day to day, and a thermometer that reads a little off is corrected at the same time. Bring a pan of water to a rolling boil, hold the thermometer in it without touching the pan, and enter the reading.
- Does this work in Celsius?
- Yes. Switch to metric and enter the recipe temperature and altitude in Celsius and metres; the subtraction is the same.