Reference to Cursor's links...those links will give you the answers you seek.
The question you ask is an extremely simplified topic that really is not that simple.
People tend to (IMO) over-concern themselves with things like:
a) what burns more fat (sometimes they mean calories)
b) what is more effective, walking, running, weights
c) how can I burn the most fat while exercising
I always explain this to people like a bank account.
You can worry yourself about "burning fat" at the time, your immediate return. Go the the ATM and withdraw $5. There you have it. But now it's gone, out of your account, you have $5 less, and when you work hard for $10, the first $5 goes towards filling that $5 withdrawal. That's like focusing/worrying about "how much fat am I burning during this walk/run?"
Then we have bank accounts (bodies) that earn interest. You make deposits which grow and grow and earn interest (ie:
building muscle). Even when you make a withdrawal (ie: burn calories), the rest of your account is busy earning interest replacing that withdrawal plus still earning money (ie: burning more calories).
But it seems people tend to be so hung up on that immediate return, the instant gratification of needing the readout that they just burned 200 calories or they spent 20 minutes in their "
fat burning zone"....without thinking that there's so much more that goes into it ... IF ... you want to maximize your all-round 24/7 "fat burning potential."
There's muscle, there's metabolism, there's intensity of your workout, there's the degree of repair required, there's efficiency of your workout and your body, there's diet (which affects your energy production), there's hormones which contribute to burning fat, or storing fat, there's the following 24-48 hours where your body is still "processing" the work load...
I think the over-simplification of searching for a readout to assign a number-value to your input of time is one of the least effective ways to gauge your workouts.