Canning Headspace Calculator

How it is calculated

The headspace is treated as a cylinder as wide as the jar at the fill line. headspace volume = π × (d / 2)² × (h / 10), where d is the inner diameter in cm and h is the headspace in mm (divided by 10 to get cm). One cubic centimetre equals one millilitre, so the result is directly in ml. fill volume = jar volume − headspace volume, and the fill percentage is fill / jar volume × 100. The jar volume is the capacity to the rim in ml. The calculator gives no result if the jar volume or diameter is zero or negative, if the headspace is negative, or if the headspace cylinder would be as large as the whole jar. A headspace of 0 is accepted and returns a 100% fill. The required headspace itself depends on the recipe and the processing method, so take it from your tested recipe.

Common mistakes

• Entering the headspace in centimetres or inches. The field is in millimetres: ½ inch is about 13 mm, not 0.5 or 1.3.
• Entering the volume up to the marked fill line as the jar volume. The field expects the full capacity to the rim.
• Measuring the outside of the glass. Use the inner diameter at the fill line, because glass walls are several millimetres thick and the outer figure overstates the volume.
• Taking the fill volume as the amount of raw food. Food that is packed tightly or shrinks during processing is a separate matter: the result is only the volume available in the jar.
• Applying one headspace to every recipe. Jams, pickles and low-acid foods use different values, so change the field for each recipe.