i have measured my terrarium (not tank) & its 30 x 12 x 12 (slightly smaller then a 20 gal, or so im told). the UTH was supposed to be 14 "L x 8 "W which would sufficiently be almost 1/2 of the terrarium's length. the UTH i ended up receiving is smaller lengthwise then my 12 in. ruler. the package said 30-40gal size but theres no way that UTH is even big enough for a 10 gallon tank. well maybe it might be, but it sure doesnt look like it. i think that UTH may have been in the wrong packaging, hey it happens. ive called reptile supply about their UTH's & they gave me the # to hagen, the company that makes their UTH's. Hagen assured me their UTH's are in fact the size they're said to be.