How to use it
- Weigh the prepared fruit and type it in Fruit weight (grams).
- Type the sugar for each part of fruit in Sugar for each part of fruit (by weight). The example uses 1, which means equal weights.
- Read the Sugar to weigh out (grams) and the Fruit and sugar together (grams).
- Before you change a recipe, read the food-safety section. A tested recipe sets the sugar.
How the sugar is worked out
The calculator multiplies the fruit weight by the ratio. A ratio of 1 gives as much sugar as fruit by weight. The ratio is only arithmetic: it does not make a recipe safe, because the sugar in jam also helps to preserve it.
sugar = fruit × ratio
fruit and sugar together = fruit + sugar- A ratio of 0.75 gives three parts of sugar to four parts of fruit.
- All amounts are in grams.
Why sugar does more than sweeten
The National Center for Home Food Preservation (NCHFP) says that sugar serves as a preserving agent, contributes flavor, and aids in gelling. It also says that too little sugar prevents gelling and may allow yeasts and molds to grow.
The NCHFP advises: do not try to reduce the amount of sugar in traditional recipes.
What this calculator does not cover
- Pectin, acid and processing time, which a tested recipe sets together with the sugar.
- Honey and corn syrup in place of sugar. The NCHFP says to use tested recipes for that replacement.
- Modified pectin products. Follow the recipes and processing times provided with each product.
- Changes to the proportions of acids and fruits. The NCHFP says they should not be altered, as spoilage may result.
Worked example: 1,500 g of fruit at a ratio of 1
Sugar = 1,500 × 1 = 1,500 g. Fruit and sugar together = 1,500 + 1,500 = 3,000 g.
| Result | Value |
|---|---|
| Sugar (grams) | 1,500.0 |
| Fruit and sugar together (grams) | 3,000.0 |
Frequently asked questions
What does a ratio of 1 mean?
It means equal weights: 1 kg of fruit with 1 kg of sugar, or 1,500 g of fruit with 1,500 g of sugar. The calculator works in grams for any amount.
Can I use less sugar in my jam?
Not in a traditional recipe. The NCHFP advises against reducing the sugar in traditional recipes. For less sugar, use a tested low-sugar recipe with the pectin it names.
Can I replace the sugar with honey?
Only in a tested recipe. The NCHFP says to use tested recipes for replacing sugar with honey and corn syrup.
Does this page check that my jam is safe?
No. It works out a weight only. For any jam you store, use a tested recipe and follow its processing times.
Sources
Figures and text last checked on Thursday, November 12, 2026.