Sand or crushed coral?

Sand for SPS / mixed reef tanks — finer grain looks better, doesn't trap as much detritus, and lets fish like wrasses sift naturally. Crushed coral was popular in the 90s for buffering but it traps gunk and is a pain to clean. Most modern reef tanks run 0.5–2 mm sand.

How deep should the bed be?

1–2 inches for a shallow sand bed (SSB) — easy to clean, no anoxic zones. 4+ inches for a deep sand bed (DSB) if you want passive denitrification, but commit fully or skip it. The unstable middle (2.5–3.5 in) gets you the worst of both.

Why is pea gravel not in the list?

Pea gravel's bulk density isn't published by any manufacturer we trust enough to put a number on. Estimates online range 90–110 lb/ft³, which is too wide a band to be useful. Use a hardware-store bag's stated weight and back-calculate from its volume if you must.

Aquarium Substrate Calculator — Pounds of Sand, Gravel, Aragonite

JavaScript is disabled in your browser, so the interactive calculator below won't run. The math, formula, and worked example are all written out further down this page under “How this is calculated.” Enable JS (or open this page in another browser) to use the live calculator.

Whether you compute by hand or in the calculator, the same caveat applies: verify against your test kit and the linked primary source before dosing. reefcalcs is reference information, not veterinary or engineering advice.

Substrate

Tank length (in)

Tank width (in)

Bed depth (in)

1–2 in is the common shallow-bed range. 3+ in is a deep sand bed.

Substrate product

Substrate needed

63.8lb

Metric

28.9kg

Volume

0.75cu ft

Bags (20 lb)

4bags

Bag density: 85 lb/ft³

Density source: caribsea.com

Gear for thisAffiliate links

CaribSea Arag-Alive Special Grade reef sand

View on Amazon →

CaribSea Pink Fiji aragonite sand

View on Amazon →

Affiliate links. As an Amazon Associate, reefcalcs earns from qualifying purchases.

How this is calculated

cubic_inches = length_in × width_in × depth_in
cubic_feet   = cubic_inches / 1728
pounds       = cubic_feet × lb_per_cuft   // by product

Densities are taken from CaribSea's Marine Substrates page. Oolitic and finer sugar-sized substrates (96 lb/ft³) pack denser than mid-grade Special Grade Reef (85 lb/ft³); chunkier crushed corals are lighter (~72 lb/ft³) because the grain gaps trap more air. Bed depth matters: under 0.5 in is cosmetic only; 1–2 in is the standard shallow reef bed; 3+ in starts behaving like a deep sand bed (DSB) with anoxic zones.

FAQ

Sand or crushed coral?: Sand for SPS / mixed reef tanks — finer grain looks better, doesn't trap as much detritus, and lets fish like wrasses sift naturally. Crushed coral was popular in the 90s for buffering but it traps gunk and is a pain to clean. Most modern reef tanks run 0.5–2 mm sand.
How deep should the bed be?: 1–2 inches for a shallow sand bed (SSB) — easy to clean, no anoxic zones. 4+ inches for a deep sand bed (DSB) if you want passive denitrification, but commit fully or skip it. The unstable middle (2.5–3.5 in) gets you the worst of both.
Why is pea gravel not in the list?: Pea gravel's bulk density isn't published by any manufacturer we trust enough to put a number on. Estimates online range 90–110 lb/ft³, which is too wide a band to be useful. Use a hardware-store bag's stated weight and back-calculate from its volume if you must.

Where to buy

Affiliate links

CaribSea Special Grade is the modern reef default — no rinse, live bacteria, 1–2 mm grain. Nature's Ocean is the budget alternative. Pink Fiji is finer for jawfish / wrasses that sift.

CaribSea Arag-Alive Special Grade reef sandLive aragonite, no rinse, 1–2 mm grain. Reef default.View on Amazon →CaribSea Pink Fiji aragonite sandPink tinge, fine grain.View on Amazon →Nature's Ocean Bio-Activ Live Aragonite sandCheaper alternative to CaribSea.View on Amazon →

Affiliate links. As an Amazon Associate, reefcalcs earns from qualifying purchases.

Share / embed this calculator

Paste this snippet into any blog or forum post that allows raw HTML to embed the calculator.

<iframe
  src="https://reefcalcs.com/embed/substrate/"
  width="100%"
  height="720"
  style="border: 2px solid #111412; max-width: 720px;"
  loading="lazy"
  title="reefcalcs Substrate Calculator"
></iframe>

Sources & references

1.
CaribSea — Marine Substrates (lb/ft³ tables)
https://caribsea.com/marine-substrates/

Last reviewed 2026-09-30