Treadmill Incline

To understand the difference between the gross and net calorie burn that the machines give you read
http://www.shapesense.com/fitness-exercise/articles/net-versus-gross-calorie-burn.aspx

With out an HRM it's the best you got. Shapesense calculators Is what i use

Try this:
http://www.walktcfitness.com/treadmill-calorie-calculator/

It's an estimation based on whether or not the treadmill you're using is correctly calibrated for speed and incline.

A.C.E. Certified Personal and Group Fitness Trainer
IDEA Fitness member
Kickboxing Certified Instructor
Been in fitness for 30 years and have studied kinesiology and nutrition

I used to use a HRM when I did my cardio and I found that if the machine you are using allows you to put in your age, weight, and height (or age and weight at the very least) --- it's calorie estimate was close enough to the estimate I got from my HRM (I had a cheaper HRM so I used the shapesense website to enter in my 'avg HR' from my monitor and calculated calories burned using that). IF the machine doesn't let you input any information then it will most likely not be very accurate.

When I was using a HRM, I knew that the calories burned that I came up with was just an estimate but I used it and ate back most of those calories and still lost weight so I figured those estimates were good enough. So sometimes it's just a little trial and error to see what works.