Enter your tank's inside dimensions to get gallons and liters, then subtract what you don't actually fill. The result links straight into the dosing calculator with your volume prefilled.
How the math works
A US gallon is defined as exactly 231 cubic inches, and one gallon is exactly 3.785411784 liters (NIST Handbook 44 (2026), Appendix C: General Tables of Units of Measurement). For a rectangular tank, multiply length 脳 width 脳 water depth in inches and divide by 231. In centimeters, length 脳 width 脳 depth 梅 1,000 gives liters. A cylinder uses 蟺 脳 radius虏 脳 depth instead.
Water weight matters for stands and floors. Reef saltwater at 35 ppt and 77 掳F weighs about 1.023 kg per liter, or roughly 8.5 lb per US gallon, before glass, rock, sand, and equipment.
| Inside dimensions (in) | Glass volume | Water 1 in below rim |
|---|---|---|
| 20 脳 10 脳 12 | 10.4 gal (39 L) | 9.5 gal (36 L) |
| 24 脳 12 脳 16 | 19.9 gal (76 L) | 18.7 gal (71 L) |
| 30 脳 12 脳 12 | 18.7 gal (71 L) | 17.1 gal (65 L) |
| 36 脳 18 脳 16 | 44.9 gal (170 L) | 42.1 gal (159 L) |
| 36 脳 18 脳 24 | 67.3 gal (255 L) | 64.5 gal (244 L) |
| 48 脳 18 脳 21 | 78.5 gal (297 L) | 74.8 gal (283 L) |
| 48 脳 24 脳 24 | 119.7 gal (453 L) | 114.7 gal (434 L) |
| 60 脳 24 脳 24 | 149.6 gal (566 L) | 143.4 gal (543 L) |
| 72 脳 24 脳 24 | 179.5 gal (680 L) | 172.1 gal (651 L) |
These are examples computed from the dimensions shown, not manufacturer specs. Retail tank names are often rounded, so measure yours.
FAQ
How many gallons is a 48 x 24 x 24 inch tank? 48 脳 24 脳 24 = 27,648 cubic inches. Divide by 231 (cubic inches per US gallon) to get about 119.7 gallons of glass volume. With the water 1 inch below the rim it holds about 114.7 gallons before rock and sand.
Should I use gross or net volume for dosing? Use the water actually in the system: tank water below the rim, plus the sump at its running level, minus what rock and sand displace. Gross (glass) volume overstates it, which makes doses too big.
How do I find how much water rock and sand displace? There is no fixed rule, so measure if you can: note how much water it takes to fill the system after aquascaping, or weigh the water you add. Otherwise enter your own estimate as a percentage and dose conservatively.