Q & A: How many miles of walking replaces a [strength] workout?
A: The best way to answer is with a question such as “how much oxygen would you need to breath to meet your water needs?” Both oxygen and water are essential for life and health, and neither is a substitute for the other. You need both. You could also ask “how much protein would I need to eat to cover my fiber intake?” Again, the honest answer is “huh?” No amount of one is going to eliminate the need for the other… in other words, the question doesn’t make sense.
Strawman
This question is (more or less) what logicians would call a “strawman.” A strawman is when people use statements or questions to substitute one thing for another. It’s a way to weasel out of something or to pretend to be “right.”
People use this trick with each other daily, and more so we use this trick with ourselves to purchase self-indulgence. We’re always the easiest person to fool.
Sleight of Hand
Here’s an example: a client has a strong family history of type 2 diabetes, high blood pressure, high cholesterol, etc. She did her InBody and wants to get her visceral fat levels down to a 9 because she doesn’t want to end up like her parents.
She puts more effort into eating better, working out more and getting more steps in. Progress happens, but it is never as fast as anyone wants it to be, and it’s always harder* than we want it to be. Instead of saying, “I don’t think I should have to work this hard,” she says, “well, I know I wanted to get my visceral fat down to a 9, but I think I look really good [pointing to the mirror].”
If the goal is to avoid her parent’s fate, and avoid burdening her children with preventable health risks, then what does “I look good in the mirror” have to do with that? Sure, the two things are likely to trend in the same direction, but that doesn’t mean one substitutes for the other.
We all want to minimize how much hard and unpleasant stuff we have to do. We all wish we could choose the consequences of our avoidance. But, like I tell my children, “wish in one hand and put an 
in the other. See which one fills up first.”
*Don’t let anyone lie to you, and tell you they know how to “hack it” or make it easy… the best hack is to quit wasting time looking for them, and just do the damn work.
And, not Or
A simple rule of thumb is that you want “and” for exercise and physical activity, and “or” for food.
Add movement on top of movement as high as your schedule will allow. However, for food we’re almost certain going to have to make trades to live within our calorie budget.
Happy 
Strength Training AND 
Walking!