Canning Altitude Adjuster
Water boils cooler the higher you live, so a canning recipe written at sea level under-processes your jars unless you correct it. Enter your altitude and method and this gives you the adjusted boiling-water-bath time, or the right pressure for a pressure canner, by the USDA rules almost every recipe online leaves out.
Read this first
This adjusts a tested recipe for your altitude. It does not tell you how long to can a food, that depends on the recipe. Always start from a current tested recipe from the National Center for Home Food Preservation or your local extension service, then bring its sea-level time or pressure here to correct it. Improperly canned low-acid foods can cause botulism, which can be fatal.
Most populated places sit under 1,000 ft. Not sure? Search your town and the word "elevation" and you will have it in seconds.
We adjust by the altitude you enter, not your town. Altitude varies too much within a place for us to guess it.
Why altitude changes canning
At sea level water boils at 212°F, but the boiling point falls roughly two degrees for every thousand feet you climb. A boiling-water bath or atmospheric-steam canner can never get hotter than its own boiling water, so at elevation the jars sit in cooler water and need more time to reach a safe internal temperature. A pressure canner does the opposite job, it raises the boiling point on purpose, so at elevation you compensate by running a higher pressure to hit the same temperature inside the jar.
The bands below come straight from the USDA Complete Guide to Home Canning and the National Center for Home Food Preservation. Boiling-water and atmospheric-steam times increase in steps as you climb. Pressure differs by gauge: a dial gauge can be set to the exact pressure for your band, while a weighted gauge only has fixed settings, so it jumps from ten pounds at low elevation to fifteen above a thousand feet.
Adjustment rules from the USDA Complete Guide to Home Canning and the National Center for Home Food Preservation (nchfp.uga.edu). This tool corrects a tested recipe for altitude; it is not itself a recipe.