Jam Pectin Ratio Calculator
Scale a jam batch: get the sugar, powdered pectin and lemon juice for your fruit weight based on how much natural pectin the fruit has.
How it works
Sugar = fruit × sugar ratio · Powdered pectin = (fruit ÷ 1 kg) × dose (0 g high / 8 g medium / 15 g low pectin fruit) · Lemon ≈ 2 tbsp per kg
Jam sets when pectin, sugar and acid come together. High-pectin fruits like citrus and apples gel with just sugar and a little lemon, while low-pectin fruits such as strawberries need added powdered pectin — roughly 15 g per kilogram of fruit. The classic 1:1 sugar-to-fruit ratio both sweetens and helps the set; low-sugar jams need a pectin specially formulated for less sugar.
Worked example
For 1,000 g of strawberries (low pectin) at a 1:1 ratio: use 1,000 g of sugar, about 15 g of powdered pectin, and 2 tbsp of lemon juice — yielding roughly five 340 g jars. High-pectin fruit like quince would need no added pectin at all.
Frequently asked questions
Which fruits need added pectin?
Low-pectin fruits — strawberries, cherries, peaches, pears — usually need it. High-pectin fruits like apples, citrus, cranberries and quince set on their own with sugar and acid.
Why add lemon juice?
Pectin needs acid to form a gel. A tablespoon or two of lemon juice per kilogram lowers the pH into the range where pectin sets, and it brightens the flavour too.
Can I make low-sugar jam?
Yes, but ordinary pectin depends on high sugar to set. For a 1:2 or lower sugar ratio, use a low- or no-sugar pectin designed for it, and follow that product’s dosing.
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This calculator is for educational purposes. Double-check important results before acting on them.