Aquarium Substrate Calculator
Work out exactly how much gravel, sand, soil, or crushed coral you need for your fish tank. Enter your tank dimensions, choose your substrate type, and get an instant result in kilograms and bags.
Calculate your substrate amount
Select your tank shape, enter the dimensions, pick a substrate type, and set your desired depth. Get the weight in kilograms and the number of standard bags to buy.
Tank & substrate details
Fill in all fields for an accurate substrate estimate
How much the front glass bows out beyond a flat front. Typically 5–12 cm. Adds ~10–15% to the footprint area.
3–5 cm for fish-only tanks. 6–10 cm for planted tanks.
Your Substrate Estimate
Weight, volume & bags to buy
Enter your tank dimensions, choose a substrate type and desired depth, then click Calculate to get your exact substrate requirement.
Which substrate is right for your tank?
The best substrate depends on your fish species, whether you keep live plants, and your water chemistry goals. Here’s a guide to the most popular options.
Coarse Gravel
The classic all-rounder. Easy to clean with a gravel vacuum, good for most community fish, and available in countless colours. Not suitable for bottom-dwellers that like to burrow.
Best for: community tanksSand
Essential for corydoras, loaches, and other bottom-dwelling fish that sift substrate. Also looks natural and shows off fish colours. Requires good circulation to avoid anaerobic dead spots.
Best for: bottom-dwellersAquatic Plant Soil
Nutrient-rich, buffered substrate specifically for planted aquariums. Lowers pH and provides months of fertiliser for roots. Lighter than gravel — use 6–10 cm depth for best plant growth.
Best for: planted tanksCrushed Coral
Raises and buffers pH and hardness — ideal for African cichlids, livebearers, and marine tanks. Not suitable for soft-water species. Also useful as a layer under regular substrate to stabilise chemistry.
Best for: cichlids, marinesBlack Volcanic Sand
Dense, fine, and striking. Neutral pH impact. Makes fish colours pop, especially bright tetras and discus. Heavier than standard sand — less likely to be disturbed by water flow.
Best for: display tanksSmooth Pebbles
Decorative and easy to maintain. Allows good water flow through the gaps. Suitable for larger fish but not ideal for burrowers. Can be mixed with finer substrate for a natural riverbed look.
Best for: larger speciesSubstrate amounts by tank size
Quick reference for coarse gravel at 5 cm depth. Actual quantities vary by substrate type and desired depth — use the calculator above for exact figures.
| Tank size | Footprint | Gravel needed (5 cm) | Approx. bags (5 kg) |
|---|---|---|---|
| Nano (30 L) | 40 × 25 cm | ~7.5 kg | 2 bags |
| Small (60 L) | 60 × 30 cm | ~13.5 kg | 3 bags |
| Medium (100 L) | 80 × 35 cm | ~21 kg | 5 bags |
| Standard (150 L) | 100 × 40 cm | ~30 kg | 6 bags |
| Large (200 L) | 120 × 45 cm | ~40.5 kg | 9 bags |
| XL (300 L) | 150 × 50 cm | ~56 kg | 12 bags |
| Display (500 L) | 180 × 60 cm | ~81 kg | 17 bags |
What to consider when choosing substrate
Substrate choice affects water chemistry, fish health, plant growth, and tank maintenance. Here are the key factors to think about before you buy.
Match your fish species
Bottom-dwelling species like corydoras, loaches, and rays need fine sand to sift through without injuring their barbels. Cichlids that excavate need heavier, coarser substrate that won’t cloud the water.
Live plants need depth
Rooted plants need 6–10 cm of nutrient-rich soil or a combined substrate (soil capped with gravel) to anchor and feed properly. Epiphytes like Java fern and anubias don’t need deep substrate at all.
Water chemistry impact
Crushed coral and calcium-rich substrates raise pH and hardness. Plant soils lower pH. For soft-water fish like discus and tetras, use inert gravel or black sand that won’t alter water parameters.
Maintenance & cleaning
Coarse gravel is easiest to vacuum — a gravel siphon pulls mulm out effectively. Fine sand must be hovered carefully without sucking it up. Plant soil is best left largely undisturbed once planted.
Buy 10–15% extra
Always order slightly more than calculated. Some substrate is lost during rinsing, settling reduces apparent depth over time, and you may want to add hardscape elements like rocks that displace substrate.
Rinse before adding
Most substrates — especially gravel and sand — need thorough rinsing before going in the tank to remove dust and fine particles that would cloud the water for days. Plant soil is the exception — don’t rinse it.
Accurate results based on real substrate densities
This calculator uses verified bulk density figures for each substrate type — not guesses. Coarse gravel, aquarium sand, volcanic sand, and plant soil all have significantly different densities, which is why a “one size fits all” approach gives wildly wrong answers.
We calculate the footprint area for your tank shape, multiply by your desired depth to get volume, then apply the substrate’s bulk density to give you an accurate weight — and round up to whole bags so you never run short.
- ✓Verified bulk density for 8 substrate types
- ✓6 tank shapes with correct area formulae
- ✓Rounds up to next full bag — no under-buying
- ✓Depth visual shows substrate vs water ratio
- ✓Customisable bag size for your preferred brand
- ✓No data stored — runs entirely in your browser
Aquarium substrate FAQs
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