Home & Construction
How much water will your tank actually hold — and how much will it weigh? Enter the dimensions for gallons, liters, substrate, and water weight.
One US gallon is exactly 231 cubic inches. A rectangular tank's volume is length × width × height in inches, divided by 231. A cylindrical tank is π × radius² × height, also divided by 231. Liters are gallons × 3.78541, and water weighs about 8.34 lb per gallon.
Measure inside dimensions if you can — glass thickness and a fill line below the rim mean a real tank holds a bit less than the outside measurements suggest. Manufacturers' nominal sizes ("55 gallon") are also approximate and usually measured on the outside, so your computed figure may land a gallon or two off the label. That's normal.
Substrate is footprint area × the depth you enter. The weight assumes dry gravel or sand at about 100 lb per cubic foot; actual products vary, and substrate also displaces water, so the tank's true water volume drops by roughly the substrate's solid volume. Weight matters: water + glass + substrate adds up fast — a filled 55-gallon setup can exceed 600 lb — so check that the stand and floor are rated for it before filling.
Why doesn't my "55 gallon" tank measure 55 gallons? Nominal names come from outside dimensions and marketing rounding. Inside measurements, glass thickness, and filling an inch below the rim commonly take 5–10% off the headline figure.
How deep should substrate be? That's a setup choice — many freshwater tanks use 1–2 inches of gravel, planted tanks often deeper. This calculator simply converts whatever depth you choose into volume and weight; it doesn't recommend depths, livestock, or stocking levels.
Does the water weight include the tank itself? No — it's water only. Add the empty tank's weight (glass tanks are heavy: a 55-gallon glass tank alone can weigh 75+ lb) plus substrate and rock for a realistic total.
More tools — Home & Construction
Board Foot Calculator · Stair Calculator · Concrete Calculator · Concrete Bag Calculator · Square Footage Calculator · Full index
Every tool on this site runs in your browser. Nothing you type is sent anywhere, stored, or tracked.