How much sugar does your fruit need? Weigh it, pick it, and get the sugar in cups and pounds at the FDA jam ratio or your own amount, the yield in jars and the gel point at your altitude.
Jam Sugar Calculator - Sugar per Pound of Fruit
How much sugar does your fruit need? Weigh it, pick it, and get the sugar in cups and pounds at the FDA jam ratio or your own amount, the yield in jars and the gel point at your altitude.
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How much sugar for jam, worked out from the fruit
Weigh the prepared fruit, pick it from the list, and the jam sugar calculator gives the sugar in cups and pounds, the weight of finished jam, how many jars to wash and the temperature that means it is done at your altitude. It starts from the ratio in the FDA standard for jam, or from the sugar you already plan to use, and it tells you how much water has to boil away for either.
Six lines on the form, one of them optional
- Fruit - 23 fruits from the two FDA groups, or other fruit. The choice sets the default sweetness of the fruit and the ratio group.
- Brix - optional. Leave it empty and the calculator uses the FDA minimum for 100% juice of that fruit. A refractometer reading from your own fruit is better, and it is required for other fruit.
- Fruit amount - in pounds, ounces, kilograms or grams, weighed after pitting, hulling and peeling.
- Sugar - the FDA ratio for that fruit, or your own amount in cups, pounds, ounces, kilograms or grams. Zero is allowed.
- Finish at - 65% soluble solids, the FDA minimum for jam, or your own target from 50 to 70%.
- Altitude and jar size - feet or meters up to 8,000 ft, and 4 oz, half-pint, 12 oz or pint jars.
From fruit on the scale to a set jam
Weigh the fruit you will cook. Stones, hulls, cores and peel come off first. The ratio in the standard is by weight, so a cup of berries is not good enough here.
Choose the sugar. The standard ratio gives the sweetness of store jam. Less sugar is your call; the result then shows how much more water the pot has to lose to reach the same set.
Check your thermometer, then boil. NCHFP asks you to test the thermometer in boiling water first. The jam is at the gel point 8 °F above that boiling point.
Have the jars ready. The jar count assumes jars filled to the rim. Headspace leaves a little over, so wash one extra.
The two FDA ratios, and which fruit goes where
The FDA standard of identity for jam and preserves (21 CFR 150.160) sets a minimum of fruit for every 55 parts of sugar by weight. Group I fruits need 47 parts, everything else 45. The last column is the sugar for one pound of fruit, which is what the calculator multiplies.
| Group | Fruits on this calculator | Fruit : sugar | Sugar per lb |
|---|---|---|---|
| I | strawberry, red and black raspberry, blackberry, blueberry, boysenberry, sour and sweet cherry, grape, elderberry, rhubarb, pineapple, crabapple | 47 : 55 | 1.17 lb |
| II | apricot, peach, nectarine, plum, pear, fig, quince, cranberry, gooseberry, red currant | 45 : 55 | 1.22 lb |
| other | any fruit on neither list ("all other cases") | 45 : 55 | 1.22 lb |
That is more sugar than fruit by weight. The same standard asks for at least 65% soluble solids in the finished jam, and at this ratio the fruit sugar plus the added sugar is close to that before the pot even heats up.
Less sugar means a longer boil
Same 4 lb of strawberries at 8° Brix, all cooked to 65%. Only water leaves the pot, so every cup of sugar you skip has to be replaced by evaporation, and the batch shrinks.
| Sugar | Cups | Jam | Water to boil off | Half-pints |
|---|---|---|---|---|
| half the fruit weight | 4 1/2 | 3.57 lb | 2.43 lb | 6 |
| three quarters | 6 3/4 | 5.11 lb | 1.89 lb | 8 |
| equal weights | 9 | 6.65 lb | 1.35 lb | 10 |
| 47 : 55, the FDA ratio | 10 1/2 | 7.69 lb | 0.99 lb | 12 |
Halving the sugar does not halve the jam, it cuts it from 7.69 to 3.57 lb, and the pot has to give up 2.43 lb of water instead of 0.99.
Where jam math usually slips
Using the sea level gel point in the mountains. Water boils lower up high, so does jam. The NCHFP table puts done at 211 °F at 5,000 ft. Cook to 220 there and the jam goes past its set and turns stiff.
Trusting a thermometer you never checked. A reading a few degrees off moves the result as much as a few thousand feet of altitude does.
Measuring fruit in cups. Whole berries, sliced peaches and crushed fruit pack differently. The ratio is weight to weight.
Mixing this with a pectin recipe. Boxed pectin recipes are tested with a fixed amount of sugar and a fixed boiling time. Use their numbers, and use this calculator for jam cooked down without added pectin.
Expecting every fruit to taste the same at one ratio. Sour cherries start at 14° Brix, rhubarb at 5.7°. With the same 2 3/4 cups of sugar per pound, rhubarb has to lose almost twice as much water.
Jam sugar questions
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