Canning Headspace & Processing Time Guide
Select your food and jar size to get the correct headspace, processing method (water bath or pressure canning), time, and pressure. Altitude adjustment included. Based on USDA/NCHFP guidelines. Nothing uploaded.
What Are You Canning?
Safe Processing Guide
Data based on USDA/NCHFP guidelines. Always use tested recipes from reliable sources. Under-processing risks botulism poisoning. When in doubt, pressure can. This tool is for reference only.
Learn more: home canning safety and processing
Acidity and the water bath vs pressure canning rule
The dividing line is acidity. High-acid foods (fruits, pickles, jams, tomatoes with added acid) can be safely water-bathed because their pH prevents botulism growth. Low-acid foods (all vegetables, meat, fish, and mixed recipes) must be pressure canned to reach 116 degrees C (240 degrees F) - the temperature required to destroy botulism spores. No amount of water bath time compensates for insufficient temperature. This guide flags each food as water bath or pressure canning required - with a safety warning for any food where the wrong method could be dangerous.
Headspace and jar sealing
Headspace is the gap between the food and the top of the jar. Different foods require different headspace: 1/4 inch (6mm) for jams and jellies; 1/2 inch (12mm) for fruits, tomatoes, and pickles; 1 inch (25mm) for vegetables and meats. Too little headspace prevents a proper seal; too much results in siphoning (food pushed out under the lid) and oxidation. The calculator shows the correct headspace for your chosen food.
Altitude adjustment for safe processing
Water boils at lower temperatures at higher altitudes, so processing times must increase to achieve the same bacterial kill. At 1,000-3,000 feet above sea level, add 5 minutes to water bath times. At 3,001-6,000 feet, add 10 minutes. For pressure canning, increase pressure by 5 PSI above 1,000 feet. The guide adjusts automatically for your altitude - enter your elevation in feet above sea level and all times and pressures adjust.
Safety and USDA testing
Canning is the one area of home food preservation where getting the process wrong has real safety consequences. Botulism is odourless, tasteless, and potentially fatal. The USDA and NCHFP publish tested safe processing times but they are scattered across dense PDF fact sheets. Always use tested recipes from reliable sources. Under-processing risks botulism poisoning. When in doubt, pressure can.
FAQ
Can I water bath can green beans?
No - never. Green beans are low-acid and must be pressure canned at 10 PSI for 20-25 minutes. Water bath canning does not reach temperatures sufficient to destroy botulism spores in low-acid foods.
How much headspace should I leave?
1/4 inch for jams and jellies; 1/2 inch for fruits, tomatoes, and pickles; 1 inch for vegetables and meats. Too little prevents a proper seal; too much causes siphoning.
How does altitude affect canning?
Water boils at lower temperatures at altitude, requiring longer water bath times. Add 5 minutes for 1,000-3,000ft; 10 minutes for 3,001-6,000ft. For pressure canning, add 5 PSI above 1,000ft. The guide adjusts automatically for your altitude.