Swimmers: accurate swimming calories burned?

balguy

when I swim , I feel that I am much hungrier the whole day. I assume that means I am burning a lot more calories than I think. I am not a professional swimmer how do I know how many calories Im burning. I assume that if Im not swimming well (perhaps kicking more than I should at times), so that might mean that Im doing more effort, also I do drills on the pool. how can I know how many calories to log as burned? I cant find an economic hr monitor for swimming?