Heavy Weightlifting

Not sure how this will look but here is a breakdown of some exercises considering a 200 pound male.

Exercise Type Calories
bicycling, stationary, 250 watts, very vigorous effort conditioning exercise 20
rowing, stationary, 200 watts, very vigorous effort conditioning exercise 19
bicycling, stationary, 200 watts, vigorous effort conditioning exercise 17
stair-treadmill ergometer, general conditioning exercise 14
rowing, stationary, 150 watts, vigorous effort conditioning exercise 13
calisthenics (e.g. pushups, situps, pullups, jumping jacks), heavy, vigorous effort conditioning exercise 13
circuit training, including some aerobic movement with minimal rest, general conditioning exercise 13
ski machine, general conditioning exercise 11
rowing, stationary, 100 watts, moderate effort conditioning exercise 11
rowing, stationary ergometer, general conditioning exercise 11
bicycling, stationary, general conditioning exercise 11
bicycling, stationary, 150 watts, moderate effort conditioning exercise 11
slimnastics, jazzercise conditioning exercise 10
weight lifting (free weight, nautilus or universal-type), power lifting or body building, vigorous effort (Taylor Code 210) conditioning exercise 10
teaching aerobic exercise class conditioning exercise 10
health club exercise, general (Taylor Code 160) conditioning exercise 9
bicycling, stationary, 100 watts, light effort conditioning exercise 9
water aerobics, water calisthenics conditioning exercise 6
calisthenics, home exercise, light or moderate effort, general (example: back exercises), going up & down from floor (Taylor Code 150) conditioning exercise 6
rowing, stationary, 50 watts, light effort conditioning exercise 6

I started lifting weights again about six months ago and am slowly increasing the weight and getting into heavy weight compound exercises (squats, dealifts, etc...) Does anybody know of a way to estimate the number of calories burned during heavy weight lifting? I have read that you can't estimate weight lifting the same as cardio.

Heart rate monitor. Although they are best used for cardio workouts, many people still use them for non-stop weight lifting sessions.

They're not accurate unfortunately. I tested it out and one workout with squats and deadlifts, I got about 600cals for 45mins total which is grossly overestimated. Azdak said it was because HRM's obiously only measure HR, whereas cals burnt is to do with Vo2. Same goes for interval training like HIIT, tabata etc.

I personally use MFP's estimates as they seem nice and conservative to me.