Amount of calories burned at X distance, speed and time

[Brodaddy]

First off, apologies in advance if this is the wrong forum (couldn't find the appropriate one)

I've been trying to calculate how much calories I'm burning (on estimate, within ~30ish calories tolerance) for some time. Many of the calculators on the internet have given me varying results. First consider my details:

Age: 20
Weight: 285 lb
Distance walked: 4 km ~ 2.5miles - Time: 40 mins
Speed (Calculated using distance and time): 6 km/h roughly 3.73 miles/h
Always sufficiently hydrated (I drink at least 2 liters of water a day, always carry a bottle with me when I'm walking)
On approx. ~1500 calories diet. Might be less but unsure.

I've gotten results from 250 calories, to 400 and one site even gave me 700 calories. Could someone with the 'know how' give me an estimate? I realize this is different from one person to another so a decent estimate would be great. Cheers :)

[slopecarver]

My fitness pal says 430 calories for your age and weight at 4mph for 40 minutes. Check out the my fitness pal app/ website

[Brodaddy]

Great thanks, I noticed it said that my daily intake to maintain my weight is 2900 calories. That seems to be quite a lot, is it accurate? Cause if its true it means I'm cutting 1400 calories a day without factoring in the exercise

[NightmareShadow]

The easiest thing is to get a good heart rate monitor like Polar. I have FT-7 and I was really surprised with how hard in reality it is to burn kkal... To burn more than 400 kkal/per hour I need to keep your heart rate 150+ and do stuff with crazy intensity. Basically, if after an hour of workout your knees and feet are sweating, than you most probably burned over 400 kkal. 40 min in gym with 12 reps per set and 30 sec resting period burned me only 270 kkal... Like a joke. I have no idea what you need to do to burn 700 per hour, my record was 537 with one hour of HIRT and average heart rate of 158/min.