how many calories do i burn while i'm working (i'd like to know for myfitnesspal)?

i use myfitnesspal to track my calories throughout the day, and it seems on the days i work i am more hungry than usual because i'm on my feet for an 8 hour shift. i'm wondering if i burn any additional calories while i'm at work? i know my calorie allotment for the day is calculated off what my resting calorie burn is, so if i'm at work walking around, i'm not really resting so i feel like that would be burning calories? i just don't know about how many i am burning so i can't add it into my tracker. i am a sales associate that is always moving around the sales floor doing tasks.