Which is accurate HRM Or Treadmills monitor?

I would go by Your HRM. That's what I do.

6.0 km/h? Then the HRM is a much more reasonable estimate.

HRM is good for measuring heart rate, that's about it. Dont rely on it to tell you how many calories you've burnt.

When you see pro athletes with heart rate monitors on you should know that they have had extensive gym time logging their power output, energy efficiency, muscle activation etc and they know what a certain heart rate relates to in terms of energy usage.

Off the shelf stuff is pretty much useless for anything other than heart rate and blood pressure. Which admittedly are very useful numbers to know.

Good luck,
JU

Studies have also shown that it is possible to estimate energy expenditure from heart rate using multivariate predictive equations derived from group data in adults “Strath , 2000; Hiilloskorpi, 2003; Dugas , 2005; Keytel , 2005)”

http://www.ncbi.nlm.nih.gov/pubmed/15966347
The correlation coefficient (r) between the measured and estimated energy expenditure was 0.913. The model therefore accounted for 83.3% (R2) of the variance in energy expenditure in this sample. Because a measure of fitness, such as VO2max, is not always available, a model without VO2max included was also fitted. The correlation coefficient between the measured energy expenditure and estimates from the mixed model without VO2max was 0.857. It follows that the model without a fitness measure accounted for 73.4% of the variance in energy expenditure in this sample. Based on these results, we conclude that it is possible to estimate physical activity energy expenditure from heart rate in a group of individuals with a great deal of accuracy, after adjusting for age, gender, body mass and fitness.

A Novel Energy Expenditure Prediction Equation for Intermittent Physical Activity
In this study the difference between a Vo2 max R1 and measuring the resting/sitting heart rate R2 and calculating from that, is the difference between 82% Accuracy R1 and 78% accuracy R2 so that is only 4% more accurate with a Vo2max calibration

In fact nearly all the studies I’ve found on-line have come to the same conclusion, using HRM for EE is accurate enough for most aerobic activities for Most of the Adult population

I have been using my HRM to track my calories burned when doing Insanity and I feel it's as accurate as it can be. If I push myself harder and go out of my "zone" then I burn more calories. If my HR is on the lower side then I don't burn as many calories. That seems to show me that it's fairly accurate.

I only ever count calorie burn when lifting weights if I have had an average of at least 118 bpm during the 40-50 minute weight session. When doing heavy weight and low reps with adequate rest then my heart rate will never average 118bpm, it will peak at 150-160 though. So, yes you can but only by basing it on an equivalent cardio burn not as a weight lifting burn. There is a very long answer as to the reason why, but best let you learn to use the HRM and get a great aerobic burn before studying anaerobic calories, glycogen storage and ATP in Type II a and b muscle fibres.

BTW at 27 your minimum cardio (fat burn zone) is comfortably an average of 125 bpm upto 136 bpm. So, if you do count weight training then the average should be at least 125 bpm.