As altitude increases, the temperature that can achieved at a given pressure will decrease.
Consequently, as altitude increases, you have to also increase the pressure inside the pressure canner to reach and maintain a desired temperature. You leave the processing time as is.
Sea level is the base
Sea level for canning purposes is deemed to be 0 to 1000 feet (0 to 300 metres). Giving processing pressure for sea level processing is the default in pressure canning recipes. (Note that some publications in some high altitude areas such as Colorado or Utah may give recipes with the pressure already adjusted specially for that area.)
A USDA bulletin from the 1970s, though dated, is still valid in its explanation of how this all works:
Atmospheric pressure is like the thickness of frosting on a cake. Where it is thickest it weighs more per square inch than where it is thin. At sea level, where the atmosphere is the thickest, it is heavier than atop a mountain.
As altitude increases, atmospheric pressure or its weight per square inch decreases. Altitude affects the boiling point of water. Where altitude is least, at sea level, water boils at 212° F [100 C]. As altitude increases the boiling point of water decreases.
The same is true in a pressure canner. Under 10 pounds pressure at sea level, water boils at 240° F [115 C]. As altitude increases, the temperature in a pressure canner at 10 pounds of pressure is less than 240°F [115 C]. This difference is enough to affect the safety of canned products at altitudes above 2,000 feet.”  Tope, Nadine Fortna. Pressure Canners, Vital for Low-Acid Foods. In: Growing, Freezing, Storing Garden Product. USDA Information Bulletin 410. 1977. Page 324 – 325.
Finding your altitude for canning
You can use Google maps to find your altitude. You can enter your entire address in: e.g 123 Queen Street, Upper Lower Bottom, Wisconsin, USA.
Dial gauge versus weighted gauge
With dial gauges, you can increase the pressure used in small increments.
With weighted gauges, because the weights are only made in 5 lb increments, you must increase the pressure in blocks of 5 lbs (35 kPa).
The following charts represent the pressure required at your altitude to reach 240 F / 115 C inside your canner. Processing time is the same at all altitudes once the correct pressure for those altitudes is applied.
Pressure Canning Meat, Vegetables, Fish, Seafood, Soup: Altitude and Pressure Chart
|Altitude feet / metres||Weighted|
|0 - 1000 / 0 - 305||10||11||69||76|
|1001 - 2000 / 306 - 609||15||11||103||76|
|2001 - 4000 / 610 - 1219||15||12||103||83|
|4001 - 6000 / 1220 - 1828||15||13||103||90|
|6001 - 8000 / 1829 - 2438||15||14||103||97|
|8001 - 10000 / 2439 - 3048||15||15||103||103|
Pressure Canning Fruit: Altitude and Pressure Chart
|Altitude feet / metres||Weighted|
|0 - 1000 / 0 - 305||5||5||35||35|
|1001 - 2000 / 306 - 609||10||6||69||42|
|2001 - 4000 / 610 - 1219||10||7||69||49|
|4001 - 6000 / 1220 - 1828||10||8||69||56|
|6001 - 8000 / 1829 - 2438||10||9||69||62|
|8001 - 10000 / 2439 - 3048||10||69|
Caution: to be clear, this second table is for fruits. See first table for all else. It is the USDA Complete Guide and So Easy to Preserve that give pressure canning alternatives for fruit. Use this altitude table only with the fruits they explicitly list for pressure canning.
Ball Blue Book. Muncie, Indiana: Healthmark LLC / Jarden Home Brands. Edition 37. 2014. Page 9.
Bernardin Guide to Home Preserving. Toronto, Canada: Bernardin Ltd. 2013. Page 12.
Bernardin. Canning at high altitudes. (Metric conversions. Accessed February 2015.)
National Presto Industries. Presto Pressure Canner and Cooker Manual. 2014. (Fruit pressure chart, page 25)
United States Department of Agriculture (USDA). Complete guide to home canning. Agriculture information bulletin No. 539. 2015. Pages 1-8 and 22 – 23.
References [ + ]
|1.||↑||Tope, Nadine Fortna. Pressure Canners, Vital for Low-Acid Foods. In: Growing, Freezing, Storing Garden Product. USDA Information Bulletin 410. 1977. Page 324 – 325.|