Aquarium Substrate Calculator
Free aquarium substrate calculator: pounds, kg, liters, and bag counts from tank footprint and depth. A 20-long needs ~21 lb of gravel per inch.
Substrate weight is footprint math: length × width × depth in inches, divided by 1,728, gives cubic feet; multiply by bulk density — about 100 lb per cubic foot for aquarium gravel — and you have pounds. A standard 20-gallon long (30 × 12 inches) needs roughly 21 lb of gravel per inch of depth. The calculator above does this for you: pick a preset tank size or enter your footprint in inches or centimeters, set a target depth (with optional front-to-back slope averaging), and choose gravel, sand, aqua soil, or crushed coral — each with a realistic bulk density. You get pounds, kilograms, and liters, plus bag counts: 5 lb and 20 lb bags for gravel and sand, 3 L and 9 L bags for aqua soil. It answers how much gravel a fish tank needs and doubles as an aquarium sand calculator. All prices below were verified in July 2026.
How much gravel do I need for a 20-gallon tank?
About 42 lb for a standard 2-inch bed in a 20-gallon long — its 30 × 12 inch footprint needs roughly 21 lb per inch of depth at gravel’s ~100 lb per cubic foot density. A 20-gallon high (24 × 12 inches) has a smaller floor and needs about 17 lb per inch, or 33 lb at 2 inches. Enter your exact footprint in the calculator above for a bag count.
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Aquarium Substrate Calculator
Key Information
| Parameter | Details |
|---|---|
| Aquarium gravel bulk density | ≈100 lb per cubic foot |
| 20-gallon long, per 1 in of gravel | ≈21 lb (30 × 12 in footprint) |
| 75-gallon at 2 in deep | 1.0 cu ft ≈ 100 lb gravel or 28.3 L soil |
| ADA Amazonia Ver.2, 9 L (Jul 2026) | $42.99 (≈$4.78 per liter) |
Frequently Asked Questions
How much gravel do I need for a 20-gallon tank?
About 42 lb for a standard 2-inch bed in a 20-gallon long — its 30 × 12 inch footprint needs roughly 21 lb per inch of depth at gravel’s ~100 lb per cubic foot density. A 20-gallon high (24 × 12 inches) has a smaller floor and needs about 17 lb per inch, or 33 lb at 2 inches. Enter your exact footprint in the calculator above for a bag count.
How much sand do I need for a 55-gallon tank?
About 57 lb for a 1.5-inch bed, the recommended depth for fine sand. A 55-gallon’s 48 × 13 inch footprint at 1.5 inches is 0.54 cubic feet, and dry sand weighs roughly 105 lb per cubic foot. Two 50 lb bags of pool filter sand ($11–25 per bag in July 2026) cover it with plenty left over — rinse thoroughly before adding.
How many liters of aqua soil do I need for a planted 20-gallon?
About 12 L at a 2-inch depth on a 20-gallon long — buy one 9 L bag plus one 3 L bag. The formula is footprint in cm² × depth in cm ÷ 1,000. A standard 60P rimless (60 × 30 cm) at 5 cm needs exactly 9 L, which is why 9 L is the flagship aqua soil bag size ($42.99 for ADA Amazonia Ver.2 in July 2026).
Are these calculators free to use?
Yes, all calculators on CalcCorp are completely free — no registration, no login, no hidden charges. Results are calculated instantly in your browser and we do not store any of your data.
How accurate are these calculations?
Our calculators use standard financial formulas updated with the latest tax rates, interest rates, and government policies for 2026. Results are accurate for planning purposes but should be verified with a professional for final decisions.
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Last updated: March 2026