Things You'll Need
- Ruler
Instructions
Measure the width of the aquarium in inches. The width is the measurement across the front. Be sure to measure from the inside of the glass; otherwise, the thickness of the tank walls will be added to the measurement and skew the calculation.
Measure the depth of the aquarium in inches. This is the measurement from front to back.
Measure the height of the aquarium in inches. This is the measurement from top to bottom. If the water is not filled to the top, just measure to the top of the water.
Multiply the width times the depth times the height.
Divide the value from step 4 by 231; 231 cubic inches equals one gallon. The resulting value is the number of gallons in the tank.