As per size. Model no.tank size power heater cap. liter cap. Um150 10” x 6½” x5½” 150 watts 400 watts 6.0 ltr. Um250 11” x 7” x 7” 250 watts 500 watts 9.0 ltr. Um400 12” x 8” x 9” 400 watts 800 watts 14.0 ltr. Um500 13” x 9” x 10” 500 watts 800 watts 18.0 ltr. Um750 15” x 9” x 10” 750 watts 1500 watts 22.0 ltr. Um1000 16” x 10” x 10” 1000 watts 1500 watts 25.0 ltr. ***** non standard as per your specification & requirement and dimension size and rating is no constraint