Calories used in manual labour

Hope this isn't a double post

I am trying to work out how many calories I have burn this week. My
job was to move 8 tons of sand in 25KG bags from pallets to 30 meters
away down stairs about 1meter high an hand them to someone. Then walk
back empty and pick up another bag. It took me about 30 minutes for
each pallet.and about 50 bags per pallet so 30 seconds round trip per
bag.

If I am 190cm tall and weigh 95KG and lifting the bags approx 2m
upwards each time

I copied this from this group

"change in potential energy (J) = change in height
(metres) * gravity (9.81) * mass (kilograms) so, 100kg's moved up
through a
height of 1 metre is approx 981 Joules = 0.981KJ = 0.236 Calories"


or 2meters x 9.81 x 25Kg is 490.5Joules

490 Joules x kcal/4184 Joules = 0.117 cal/rep

320 bags is only 37.44 Calories ?


So I'm not even sure how it could be that low anyone have some spare
time to help I would be grateful