How much live rock do I need per gallon?

The long-standing guideline is roughly 1 to 1.5 pounds of live rock per gallon of tank volume, with the lower end for porous, lightweight rock and the higher end for denser rock. This tool applies that range and adjusts it for rock density.

Why does rock type change the amount?

Live rock works by surface area and structure, not raw weight. Dense ceramic or dry rock packs more mass into the same shape, so you need fewer pounds to build the same aquascape, while light porous rock needs more pounds for equivalent structure.

Should I count my sump or just the display?

Base the calculation on the display tank you are aquascaping. Many reefers actually run less rock in the display for flow and use additional biomedia in the sump, so treat the result as an upper guide rather than a strict minimum.

Is more live rock always better?

No. Modern reefkeeping trends toward less rock for better water flow and open aquascapes, relying on the rock surface plus sump filtration for biological capacity. Use the range as a guide and lean lighter if you want open scaping and strong circulation.

How do I estimate the cost?

Enter your local price per pound for the rock type you are buying and the tool multiplies it by the recommended weight. Cured live rock costs more than dry rock, which you cure yourself over weeks, so price the specific product you intend to use.

Aquarium Live Rock Amount Calculator

Stocking a reef tank starts with the rock, and the classic rule of thumb scales the amount to tank volume. This calculator applies that guideline, adjusts it for how dense your chosen rock is, and estimates the cost from your own price.

How it works

The baseline is the familiar pounds-per-gallon range, scaled by a density factor for the rock type:

gallons   = volume (converted from litres if needed)
base low  = gallons × 1.0 lb
base high = gallons × 1.5 lb
adjusted  = base × density factor
            porous ≈ 1.0, standard ≈ 0.85, dense ceramic ≈ 0.65
cost      = recommended weight × your price per lb

Denser rock builds the same aquascape with fewer pounds, so the recommended weight drops as density rises. The recommended figure is the midpoint of the adjusted range.

Notes and tips

Treat the result as an upper guide, not a target — current reefkeeping favours less rock for better flow and open aquascapes, with extra biological filtration in the sump. If you are using dry rock, you will cure it yourself over several weeks before it becomes biologically active, which is cheaper than buying fully cured live rock but slower to mature. Price the exact product you intend to buy, since cured live rock and dry rock differ sharply in cost per pound.