Cooking fails most often on measurement, not on skill. A recipe that works in one kitchen fails in another because the pan, pot or scoop was a different size. This free tool takes jar volumes out of the guessing game. It turns a jar height and diameter into millilitres, cups and fluid ounces, so you can plan preserving, pickling and pantry storage without guessing, right in your browser, with no account and no download.
The maths behind the tool is simple and honest: a jar is a cylinder, so its volume is pi times the radius squared times the height. Small changes in diameter matter more than small changes in height, because the radius is squared. A jar 8 centimetres wide and 12 centimetres tall holds about 600 millilitres, while a jar 10 centimetres wide and the same height holds about 940 millilitres.
standard preserving jars cluster around familiar sizes: about 250 millilitres for small jams, 500 millilitres for everyday sauces and pickles, and around 1 litre for large batches and fermented vegetables. If your jar does not match a standard size, this tool gives you the real number, which matters when a recipe says it fills four 500 millilitre jars and you own something else.
Use the tool before you shop, not after. for preserving, leave 1 to 2 centimetres of headspace at the top of the jar. Food expands as it heats, and without headspace the seal can fail or the jar can leak in the water bath. For dry storage, fill jars as full as you like: less air means slower staling for flour, rice, spices and dried beans.
Watch out for the usual trap: the most common mistake is measuring the outside of a thick glass jar and forgetting the glass itself. Very thick jars hold a little less than the outside size suggests, so treat the result as a close guide and check with water for exact preserving batches. Another mistake is reusing jars with damaged rims for canning: a chipped rim will not seal, whatever the volume.
Here is how a typical session goes. Open the tool, enter the numbers you already know, and read the result before you change anything else. Then change one input at a time and watch how the result moves: that single habit teaches you more about sizes than any table, because you see which input matters most. Try your own real numbers, not just the defaults, and compare the result with the pan, pot or scoop sitting in your cupboard right now. If the result surprises you, measure again: a wrong diameter or a guessed height is the usual cause, not a fault in the tool.
Plan the whole job around the number the tool gives you. If the volume changes, the cooking time, the dish size and the serving count all change with it, so check them together instead of fixing one and forgetting the rest. Write the result on the recipe card, so next time you cook the same dish you start from the right number instead of measuring again.
This tool suits beginners and experienced cooks alike. Beginners get a safe number without learning formulas, and experienced cooks get a fast check before scaling a recipe up for a party or down for two people. Both groups avoid the same waste: food that overflows, dishes that come up short, and batches that bake unevenly.
Save this page for your next cooking session. The tool is free, works on a phone or a computer, and needs no sign-up. Enter your numbers, read the result, and cook with a plan instead of hoping the size works out.
Versión en español de esta herramienta