So the way I do it, I spray my whole lawn with water like I'm applying product. And that's how much water I need for a full blanket application. Then I measure how much product I need for my size lawn and dump it in.
It ended up being close to 1 gallon per k of water anyways, but I feel this is less difficult to understand and it allows for slight changes in walking pace. If you want to walk slower, you'll end up using more water but the amount of product doesn't change.