I've been looking for this myself, I just got done reading on another site that 1.66 lbs is equivalent to a quart, based off a standard bushel and how many quarts are in one, divided by poundage... Another site said 2.2 lbs.. However, that is the conversion kilograms. 2.2 lbs in a kg so I wouldn't trust that one. So the math on 4 quarts using the 1.66 guide you would end up with needing 6.64 lbs of tomatoes.