Canning Altitude Calculator: Time & Pressure Adjustment

Water boils cooler as you climb: about 212°F at sea level but only around 198°F at 7,000 feet. Canning processes are timed and pressured for the heat that actually kills spoilage organisms and, in low-acid foods, botulinum spores — so at altitude you must add time or add pressure to make up the difference. This tool reproduces the tested adjustment tables published by the USDA Complete Guide to Home Canning and the National Center for Home Food Preservation (NCHFP). It looks the numbers up by altitude band; it does not calculate or interpolate them.

Which adjustment applies depends on the method. In a boiling-water bath (for high-acid foods like most fruits, jams, and salsas) the pressure can't change, so you add processing time: 5 to 20 minutes for a recipe timed at 20 minutes or less, and 10 to 40 minutes for a longer one, stepping up by altitude band. In a pressure canner (required for low-acid foods — vegetables, meats, most soups) the time stays the same and the pressure rises. A dial gauge adjusts in fine steps — 11, 12, 13, then 14 pounds as you climb through the bands to 8,000 feet. A weighted gauge can't fine-tune, so it jumps from 10 pounds at or below 1,000 feet to 15 pounds above it.

Start from a tested recipe and apply the adjustment to it — the base time and base pressure come from your recipe, not from this page. Never reduce a time or a pressure. If your elevation is above the highest tested band, the tool will not guess a number; check with NCHFP or your local Extension office. Food safety depends on following a tested process exactly.