ill have to measure my Tub and UTH dimmesions when i get home. I know they def do not cover 1/3 of the tub. I have them on a thermostat connected to the heat pad outside the tub, a probe inside the tub under the newspaper and then i double check the probe readings every day or two with my heat gun. My belly temp on my BP is 92, because for some reason it either wants to be at 86 or 95. My boa is at 89. The only problem i have is that my boa is always cold to the touch while my BP is always nice and toasty and comfy