Jam & Marmalade Calculator: How Many Jars Will It Make
A glut of fruit is easy to weigh and hard to picture as jars on a shelf. Enter what you have, pick the preserve you are making and the jars you own, and read back how much it will yield and how many jars that fills. Useful when:
- Buying jars before you start: find out how many you need while the shops are still open.
- Working from a tree or a tray: enter a count of whole fruit instead of a weight.
- Working from a recipe: divide the fruit you have by what the recipe calls for, then scale the rest of the ingredients by that number.
- Making marmalade: citrus yields far more per kilo than a berry jam, and the calculator shows by how much.
- Budgeting the sugar: see the sugar the batch needs before you commit to the fruit.
- Comparing jar sizes: enter jars in millilitres, centilitres, litres, cups, pints or quarts.
Work out your batch
Your batch:
6 jars
- Finished preserve
- 2.52 L
- Finished weight
- 3.35 kg
- Sugar needed
- 2 kg
- Each jar holds
- 475 ml
Low in pectin. Add lemon juice or sugar to get it to set.
Fruit you can preserve
| Fruit | How it jams |
|---|---|
| Apple | Apple carries enough pectin and acid to set firmly on its own, which is why it turns up in so many other fruits' recipes. Windfalls and cores make a clear jelly. |
| Apricot | Apricot runs low on both pectin and acid, so lemon juice earns its place here. The colour stays bright, and dried fruit gives a thicker, darker preserve. |
| Blackberry | Riper blackberries will have less pectin, so if your blackberries are under-ripe the jam should set without help; with more ripened fruit, add lemon or chopped apple to help it set. The jam will contain the pips, so if you want a smoother texture, strain the pulp before setting. |
| Blueberry | Blueberry holds less pectin than its firm skin suggests, so a batch usually wants added pectin or a squeeze of lemon. The colour stays deep and the flavour mild. |
| Fig | Fig is very sweet with almost no acid, so lemon juice does double duty on the set and the balance. Chopped fruit gives a thick, seedy preserve. |
| Grapefruit | Makes a bitter, loose-set marmalade that benefits from added lemon. Remove most of the white pith or the result turns harsh. |
| Grapes | Grapes are strained for jelly rather than crushed for jam, since the skins and pips stay coarse. There is enough natural pectin in them that a classic grape jelly sets without any added. |
| Kiwi | Kiwi has its own version of pineapple's enzyme problem, so it needs a short simmer first and added pectin after. Chopped flesh keeps the green flecks. |
| Lemon | The peel and pips carry enough pectin to set marmalade without help. Lemon is also the standard acid added to low-pectin jams. |
| Lime | Sets readily thanks to the high pectin in the peel and pith. Lime marmalade is sharper than orange and takes a longer boil to soften the peel. |
| Mango | Mango jam wants lemon juice and usually added pectin. Slightly under-ripe fruit sets better than fully ripe. |
| Nectarine | Behaves like peach and needs the same lemon juice and added pectin. The skin stays on and gives the jam a pink tint. |
| Orange | Sweet oranges make a mild marmalade and need lemon juice for a reliable set, while bitter Seville oranges set on their own. The peel is shredded and simmered until soft before the sugar goes in. |
| Peach | Peach needs lemon juice and often added pectin, having little of either itself. The skins slip off easily after a short blanch. |
| Pear | Pear is sweet and low in acid, so it needs lemon juice both to set and to keep the flavour from going flat. It works best alongside a sharper fruit like apple. |
| Pineapple | Pineapple carries bromelain, an enzyme that breaks down a set, so cook it through before the sugar goes in. It also needs added pectin and a good squeeze of lemon. |
| Plum | High in both pectin and acid, so plum sets easily and is one of the most forgiving jams to make. The stones can be simmered in a muslin bag for extra pectin. |
| Pomegranate | Made as a jelly from the strained juice, since the seeds are too hard to leave in. Pomegranate jelly needs added pectin to set. |
| Raspberry | Raspberry sets on its own pectin and acid, so it is a good option to start on if you have never made jam. If you don't like the seeds in the final product, sieve half the pulp and stir it back in to keep the flavour with less crunch. |
| Strawberry | Strawberry makes the classic jam and the trickiest set, since the fruit holds very little pectin. Keep the boil short and small berries will stay whole in the jar. |
The Batch That Ran Out of Jars
We visited a friend for lunch and left with a tray of home-made marmalade. He lives on a large property with several orange trees, and rather than let the ripe fruit go to waste he had picked the lot and preserved it. Marmalade is a favourite of his. The one thing that caught him out was the quantity. He had estimated how much the fruit would make. The estimate fell well short, and he had to order more jars part-way through bottling. That is a common way to get caught, and it happens because the obvious mental model is wrong: people scale the yield off the fruit, when the yield actually scales off the sugar.
Sugar Sets the Yield, Not Fruit
Jam and marmalade are finished when they reach about 65 percent soluble solids, the set point a cook hits at 104 to 105 degrees Celsius. Sugar survives the boil and water leaves, so whatever water went into the pan, the finished mass lands near the total sugar divided by 0.65. That single relation explains the marmalade surprise. A berry jam adds its own weight in sugar, while a Seville marmalade adds twice the fruit weight, so the same kilo of fruit returns roughly 1.7 kg as jam and 3.2 kg as marmalade. The litres of water a marmalade recipe calls for change how long you stand over the pan, and change nothing at all about how many jars you need.
Headspace and Why Jars Hold Less Than They Say
A jar sold as 500 ml does not take 500 ml of preserve. You leave roughly a centimetre at the neck so the lid seals properly and the contents have somewhere to go, which costs about 25 ml whatever the jar size. This calculator works on that basis, so a 500 ml jar counts as 475 ml and a 250 ml jar as 225 ml. If your jars are marked in another unit, the volume converter will translate them first.
Frequently Asked Questions
- How much jam does 1 kg of fruit make?
- At the traditional one-to-one sugar ratio, 1 kg of fruit makes about 1.68 kg of jam, which is roughly 1.26 litres. The final weight comes from the sugar rather than the fruit: 1 kg of added sugar plus the fruit's own 90 g of natural sugar gives you 65 percent solids, for a regular jam set. That gives two full 500 ml jars and a third about two-thirds full. Open the strawberry converter
- Why does marmalade make more than jam?
- Marmalade recipes add 1.5 to 2 kg of sugar per kilo of fruit against 1 kg for a berry jam, and the yield tracks the sugar rather than the fruit, so citrus gives far more per kilo. A kilo of Seville oranges makes about 3.22 kg of marmalade, close to double the 1.68 kg the same weight of fruit gives for a traditional jam. The water added to soften the peel boils off and does not change the total. Open the orange converter
- How many jars will my batch need?
- Divide the finished volume by what one jar actually holds, then round up. A 500 ml jar takes about 475 ml of preserve once you leave a centimetre of headspace at the neck, so 2 kg of strawberries making 2.52 litres needs six jars. Buy one or two spare for safety, as a batch that sets slightly loose fills more than a firm one.
- How much sugar does a jam batch need?
- Traditional jam uses equal weights of fruit and sugar, so 2 kg of fruit takes 2 kg of sugar. A soft-set or reduced-sugar jam drops to about 0.7 kg per kilo of fruit and gives a looser result that keeps for less time once opened. Marmalade runs higher at 1.5 to 2 kg per kilo, which balances the bitterness of the peel and is the reason it yields so much more. Open the sugar converter
- What size jars are best for jam?
- Most home preserves go into jars between 190 ml and 500 ml. Smaller jars are easier to give away and get eaten before the seal has been open long, while larger ones save time at the bottling stage. Leave about a centimetre of headspace whatever the size, so a 500 ml jar holds around 475 ml and a 250 ml jar around 225 ml.
- Do I need to add pectin to my jam?
- You need it only for the low-pectin fruit. Apples, plums, lemons and limes carry enough of their own to set unaided, while sweet oranges and grapefruit sit in the middle and want a squeeze of lemon. Strawberries, peaches, pears and figs carry very little, so they need lemon juice, jam sugar, or a high-pectin fruit alongside them. The calculator names the pectin level for whichever fruit you pick. Open the pectin converter
- Can I work from a count of whole fruit?
- Yes. Switch the amount to whole fruit and pick a size, and the calculator weighs the count for you. A medium orange is 180 g, so 50 of them come to 9 kg, which as sweet-orange marmalade makes about 22 kg of preserve and fills 35 jars of 500 ml. Counting is usually easier than weighing when the fruit comes off a tree.
More conversions
Convert ingredient measurements or fresh fruit and vegetables.
Updated