I checked my thermacell replacement box last night. Sure enough it says 4 hrs. I am just going by the bugs. Most days I run the same pad all day with no problem. Most days I just replace the pad the next morning. A few times I have been running low on pads and the pad from yesterday worked until about lunch time before I really noticed it not working. Maybe those days the bugs weren't out until lunch time, but I can say I have never changed a new pad during a single hunting day. Another possible factor is during the warmer weather I do use Sawyer's for the ticks. It all boils down to during bug weather the thermacell is as important in the woods as bullets or arrows. Don't leave home without them.