Jam reaches its setting point at 220 °F (104.4 °C) at sea level: 8 °F (4.4 °C) above the boiling point of water, according to the National Center for Home Food Preservation (NCHFP). Higher up, water boils cooler, so the target drops, to 216 °F at 2,000 ft and 211 °F at 5,000 ft. Enter your altitude, or the temperature your water boils at, then check the set with a cold plate.
Setting point · NCHFP temperature test
At sea level
220 °F (104.4 °C)
Boil the jam until it reaches this temperature, then check with a cold plate.
No temperature neededPackaged-pectin recipes boil hard for 1 minute instead.
Test your thermometer in boiling water first, as NCHFP advises. Using that reading plus 8 °F (choose “My boiling water” above) also allows for a thermometer that reads a little high or low.
Read it upright at eye level, with the bulb covered by jam but not touching the pan.
British recipes often give 105 °C, a little above NCHFP’s 220 °F (104.4 °C). Either way, back it up with a plate or spoon test.
NCHFP’s temperature test gives these targets, measured with a jelly or candy thermometer. The Celsius and metre figures are our conversions:
Altitude
Setting point
Sea level
220 °F (104.4 °C)
1,000 ft (305 m)
218 °F (103.3 °C)
2,000 ft (610 m)
216 °F (102.2 °C)
3,000 ft (914 m)
214 °F (101.1 °C)
4,000 ft (1,219 m)
212 °F (100 °C)
5,000 ft (1,524 m)
211 °F (99.4 °C)
6,000 ft (1,829 m)
209 °F (98.3 °C)
7,000 ft (2,134 m)
207 °F (97.2 °C)
8,000 ft (2,438 m)
205 °F (96.1 °C)
NCHFP sums it up as “for each 1000 feet of elevation above sea level, subtract 2 degrees F”, though its own table drops only 1 °F between 4,000 and 5,000 ft. Between rows, the calculator draws a straight line and rounds to the nearest half degree, so 2,500 ft gives 215 °F. Above 8,000 ft the table stops: measure your boiling water and add 8 °F, which works anywhere. British recipes often give 105 °C, a fraction above the US figure; both are close enough that the plate test settles it.
Four ways to tell if jam is set
The thermometer is the most dependable test, according to NCHFP; the others confirm it.
Thermometer. Clip a jelly or sugar thermometer upright in the pan so the bulb is fully covered by jam but doesn’t touch the bottom, and read it at eye level. Before you start, check it in boiling water. NCHFP calls this the most dependable of its three tests.
Cold plate, or wrinkle test. NCHFP’s version: pour a little boiling jam onto a plate and put it in the freezer for a few minutes. If it gels, it’s done. Take the pan off the heat while you wait, or the jam keeps cooking. British cooks chill a few saucers before they start, spoon on a little jam, leave it for about 30 seconds and push it with a finger: if the surface wrinkles and doesn’t flood back, it is ready (BBC Good Food).
Spoon, or sheet test. Dip a cool metal spoon into the boiling jam and lift it out of the steam so the syrup runs off the side. At first the drops are light and syrupy; as the jam cooks they get heavier and fall two at a time. When two drops run together and sheet off the spoon, it has reached the jellying point.
Flake test. The British name for much the same thing: dip a spoon, let the jam cool a little, then pour it slowly back. At setting point the drops run together into a hanging flake (BBC Food).
Why altitude changes the setting point
Jam sets when enough water has boiled off to concentrate the sugar, and the temperature of the boiling jam tells you how concentrated it is. That temperature is relative to the boiling point of water where you are. USDA’s table puts water’s boiling point at 212 °F at sea level, 208 °F at 2,000 ft, 204 °F at 4,000 ft, 201 °F at 6,000 ft and 197 °F at 8,000 ft. Jam cooked to the sea-level 220 °F in a mountain kitchen would be over-boiled and stiff, which is why the target moves down with the water. High Nestle works out the boiling point of water for any altitude.
Jelly, marmalade and fruit butter
The same 8 °F rule covers jelly and jam made without added pectin, for which NCHFP prints the same altitude table, and NCHFP’s citrus marmalade, which is boiled until it measures 8 °F above the boiling point of water, 220 °F at sea level. Fruit butter is different: it isn’t boiled to a set at all. The USDA apple butter is done when a spoonful held away from the steam for 2 minutes stays mounded on the spoon, or when a little spooned onto a plate doesn’t leave a rim of liquid around its edge.
Worked examples
Sea level: 220 °F (104.4 °C).
2,500 ft (762 m): halfway between 216 °F and 214 °F, so 215 °F (101.7 °C).
1,600 m: 5,249 ft, a quarter of the way from 211 °F to 209 °F: 210.5 °F (99.2 °C).
Your water boils at 203 °F: 203 + 8 = 211 °F (99.4 °C), whatever your altitude.
Common mistakes
Thermometer touching the pan. NCHFP says the bulb must be covered by jam but must not touch the bottom.
Leaving the jam boiling during a plate test. It overshoots and turns stiff.
Judging it hot. NCHFP reminds you to allow for thickening during cooling, and some jams take up to 2 weeks to set completely.
Testing a pectin jam. Recipes with packaged pectin boil hard for a set time, usually 1 minute, and need no setting test.
Using the sea-level figure up a mountain. Check the table or your boiling water.
220 °F (104.4 °C) at sea level, which is 8 °F above the boiling point of water, according to NCHFP. Many British recipes say 105 °C. At altitude the setting point is lower: 216 °F at 2,000 ft and 211 °F at 5,000 ft.
How do you do the wrinkle test for jam?
Chill a few saucers in the freezer before you start. Take the pan off the heat, spoon a little jam onto a cold saucer, leave it about 30 seconds and push it with your finger. If the surface wrinkles, it is set; if not, boil a little longer and test again.
How do I find the setting point at high altitude?
Boil a pan of water, read its temperature and add 8 °F (4.4 °C). NCHFP’s table gives the same answer by altitude, from 218 °F at 1,000 ft down to 205 °F at 8,000 ft.
Do I need a thermometer for jam made with pectin?
No. NCHFP notes that added pectin removes the need to test hot jams for gelling: you bring the jam to a full rolling boil and boil hard for the time the recipe gives, usually 1 minute.
Is the spoon test or the plate test better?
NCHFP rates the temperature test as the most dependable. The plate and spoon tests are useful checks, especially if you aren’t sure your thermometer is accurate.
Sources
Setting point, the 8 °F rule, Table 1 and the three tests: NCHFP, Testing Jelly without Added Pectin (adapted from So Easy to Preserve, 6th ed., 2014; checked 5 November 2026).