Live Rock Calculator
Live rock is your saltwater tank's biological filter. Enter your tank size and setup type — we'll tell you how many pounds you need.
Calculate live rock amount
How live rock sizing works
Live rock's porous structure hosts the nitrifying bacteria that process fish waste — it's the biological filter of a saltwater tank. The long-standing guideline:
- 1.0–1.5 lb per gallon — FOWLR (fish only with live rock)
- 1.5–2.0 lb per gallon — reef tanks, which benefit from extra filtration and coral mounting space
Very porous rock (like pukani) does the same filtration job at the lighter end of the range; dense rock needs the heavier end.
Live rock tips
- Cure new live rock before adding it — die-off during shipping causes an ammonia spike.
- Aquascape with gaps and arches for water flow; a solid wall of rock traps detritus.
- Save money with dry base rock seeded by a few pounds of true live rock — it becomes fully "live" in a few months.
- Rinse rock in saltwater, never freshwater — freshwater kills the beneficial organisms.
Frequently asked questions
How many pounds of live rock for a 55 gallon reef?
About 80–110 pounds (1.5–2 lb per gallon). Very porous rock can go lighter; dense rock should go heavier.
Live rock vs dry rock — which is better?
Dry rock is cheaper and pest-free, and becomes biologically "live" within months. Live rock cycles faster but can carry unwanted hitchhikers. A mix of both is the popular compromise.
Does live rock replace my filter?
It replaces biological filtration, but you still want mechanical filtration, a protein skimmer and water flow. Think of rock as the foundation, not the whole system.
How do I cure live rock?
Keep it in heated, circulating saltwater with a skimmer for 2–4 weeks, testing ammonia until it reads zero. Then it's safe to add to the display tank.