How do I estimate jam yield from fruit and sugar?

The approximate yield of jam is about 85% of the combined weight of fruit and sugar. The remaining 15% is water that evaporates during the boiling process. So 1kg fruit + 1kg sugar gives roughly 1.7kg (1,700g) of jam.

Should I fill jars right to the top?

Leave about 5mm of headspace at the top of each jar. This allows for a proper vacuum seal to form as the jam cools. The lid should create a slight concave shape when sealed properly, indicating a good seal.

What jar sizes are most common for jam?

The most popular size for homemade jam in the UK is the 454ml (1lb) jar. For gifts, the 227ml (8oz / half-pint) jar is a nice size. Standard hexagonal jars are typically 200ml or 340ml. All jars should have new, unused lids for a proper seal.

How much does jam weigh compared to its volume?

Jam is denser than water due to the dissolved sugar. The density is approximately 1.3g/ml. So a 454ml jar holds about 590g of jam. This is why a "1lb jar" (454ml) actually holds more than 1lb (454g) of jam by weight.

How many jars should I prepare for sterilising?

Always prepare 1-2 more jars than you think you will need. Yield can vary depending on how long you boil the jam and the water content of your fruit. Having spare sterilised jars ready avoids scrambling if you have more jam than expected.

BakeCalcs

Jam Jar Quantity Calculator

Calculate how many jars a batch of jam will fill based on fruit weight, sugar weight, and jar size.

Fruit Weight

Sugar Weight

Jar Size

How We Calculate This

This calculator estimates the total yield of your jam batch based on the combined weight of fruit and sugar, accounting for approximately 15% water loss during boiling. It then calculates how many jars you need based on the yield volume and your chosen jar size.

The Calculation

Total yield (weight) = (Fruit + Sugar) x 0.85
Total yield (volume) = Yield weight / 1.3 (jam density)
Jars needed = Yield volume / Jar size (rounded up)

Tips

Always prepare 1-2 extra sterilised jars
Leave 5mm headspace when filling
Fill jars while jam is still hot for the best seal

Frequently Asked Questions

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Last updated: February 2026

All calculations are based on standard ratios and conversions. Results may vary with specific ingredients, equipment, and conditions.