Hi,
I have a query and wonder if you could help.

What is the exact method to know how many calories you have burnt by walking if you know:-
1) the time spent
2) your walking speed
3) your weight

Thank you.

Take a look at this topic and also this site

Calories are a value of energy. Therefore, the only variables which contribute to how many calories are expended are:

1. The weight of the person
2. The distance over which they move

The speed / or time spent are of no significant value, although most formulas give a nominal value to speed because the body does operate slightly less efficiently at higher speeds. But the difference between walking and running a mile is negligable.

There's a cool calorie calculator coolrunning.com

I bought a pedometer. It averages about 100 calories burned per mile walked. I know it doesn't sound like much much you are also boosting your metabolism. I know because I am doing it. I am walking, exercising and still eating what I want. It works. I lost 6 pounds and I still have kept it off. All of my clothes fit better. I have lost inches. Walking is great.