Canning day always starts with the same guess: how many jars is this actually going to make? Underestimate and you're short on jars mid-batch. Overestimate and you've sterilized more than you need. There's a real answer here, and it comes down to a yield ratio that varies by what you're actually canning.
Yield Depends on What's Going Into the Jar
Whole tomatoes pack differently than tomato sauce, and green beans pack differently than sliced peaches. As a rough guide, about 21 pounds of tomatoes makes 7 quarts whole, while sauce takes noticeably more raw tomatoes per jar since you're cooking down volume as you go. These numbers move around based on ripeness and variety, so treat any yield estimate as a planning number, not a promise.
Altitude Changes Your Processing Time, and It's Not Optional
This is the part that actually matters for food safety, not just convenience. Water boils at a lower temperature as elevation increases, around 212°F at sea level but closer to 203°F by 5,000 feet. A boiling water bath can never get hotter than boiling, so at higher elevations, that lower temperature means less heat actually penetrating the jar in the same amount of time. The fix is straightforward: add time to your recipe's base processing time based on your altitude, typically 5 extra minutes for elevations between 1,000 and 3,000 feet, more as you go higher.
This Only Covers Water Bath Canning
Boiling water bath canning works for high-acid foods like tomatoes, fruit, pickles, and jam. Low-acid vegetables and any meat require pressure canning instead, with its own altitude adjustments based on pressure rather than time. That's a different process with different safety margins, and it's worth using a current, tested recipe from the USDA or National Center for Home Food Preservation rather than guessing.
I built a free canning batch calculator that estimates your jar yield based on what you're canning and how much you've got, plus tells you exactly how many minutes to add to your recipe's water bath time for your specific altitude.
Whatever you're growing this season, grow it well.