This measurement is going to depend on a lot of things, the first being what kind of tomatoes that you use. Romas will be more fleshy and create a thicker sauce, while beefsteak will have more juice. Plan for 6 quarts and use more or less jars as needed.

Lets see… 1/2″ of headspace is adequate but I like to err on the side of caution with 1″, tomatoes are naturally high in acidity, processing time varies on jar size, larger jars for longer and smaller jars for shorter times, just be sure that the snap lids “pop”. We make this recipe every year in the fall for the last dozen years or so. It is shelf stable for a year but usually doesn’t last that long.

1 qt = 1 L = 1 kg of water (or tomatoes)

Assuming all of the other ingredients add up to about a kg, wouldn’t starting with just 4.5 kg of tomatoes make a very thin sauce? The total mass of all ingredients is only 5.5 kg, which might barely fill the 6 quart jars.

No peeling needed as they get blended in with the sauce. You can blanche the tomatoes and remove the peels but its not needed.

The pH of this tomato sauce is about 4.5. Tomatoes are highly acidic making them safe to can using the water bath method. Be sure to process them for the directed length of time and test that the snap lids have popped. If you are unsure, you can always use a pressure canner as well. More tips are in my Complete Guide to canning.