Free tool
Stocking & tank-size calculator
The number-one beginner mistake is too many fish in too little water. Tell us your tank and your wish-list — we'll check each fish against its fact-checked minimum tank and group size, flag any clashes, and give you an honest read on how full the tank is.
Adult size & minimum tank, per fish
Plan for the adult, not the juvenile in the shop. Every figure is from that fish's fact-checked care guide — shortlist here, then run your wish-list through the calculator above for the honest capacity read on your tank.
| Fish | Adult size | Minimum tank | Kept as |
|---|---|---|---|
| Amano Shrimp | ~5 cm | 40 L (11 gal) | Shoal of 3+ |
| Angelfish | ~15 cm | 120 L (32 gal) | One (or a pair) |
| Apistogramma | ~7 cm | 55 L (15 gal) | One (or a pair) |
| Assassin Snail | ~2.5 cm | 8 L (2 gal) | One (or a pair) |
| Bamboo Shrimp | ~9 cm | 75 L (20 gal) | One (or a pair) |
| Betta | ~7 cm | 19 L (5 gal) | One only |
| Black Neon Tetra | ~4 cm | 75 L (20 gal) | Shoal of 8+ |
| Black Phantom Tetra | ~4.5 cm | 75 L (20 gal) | Shoal of 8+ |
| Black Skirt Tetra | ~6 cm | 68 L (18 gal) | Shoal of 12+ |
| Blood Parrot Cichlid | ~20 cm | 200 L (53 gal) | One (or a pair) |
| Boesemani Rainbowfish | ~11 cm | 108 L (29 gal) | Shoal of 6+ |
| Bolivian Ram | ~8 cm | 182 L (48 gal) | One (or a pair) |
| Bristlenose Pleco | ~13 cm | 75 L (20 gal) | One (or a pair) |
| Cardinal Tetra | ~3.5 cm | 40 L (11 gal) | Shoal of 6+ |
| Celebes Rainbowfish | ~8 cm | 75 L (20 gal) | Shoal of 8+ |
| Celestial Pearl Danio | ~2 cm | 30 L (8 gal) | Shoal of 6+ |
| Cherry Barb | ~5 cm | 54 L (14 gal) | Shoal of 6+ |
| Cherry Shrimp | ~4 cm | 8 L (2 gal) | Shoal of 10+ |
| Chili Rasbora | ~2 cm | 41 L (11 gal) | Shoal of 8+ |
| Clown Loach | ~40 cm | 648 L (171 gal) | Shoal of 5+ |
| Clown Pleco | ~9 cm | 75 L (20 gal) | One (or a pair) |
| Common Goldfish | ~30 cm | 190 L (50 gal) | One (or a pair) |
| Common Pleco | ~60 cm | 284 L (75 gal) | One (or a pair) |
| Congo Tetra | ~8 cm | 108 L (29 gal) | Shoal of 6+ |
| Convict Cichlid | ~15 cm | 90 L (24 gal) | One (or a pair) |
| Corydoras (bronze) | ~7 cm | 72 L (19 gal) | Shoal of 6+ |
| Croaking Gourami | ~6 cm | 54 L (14 gal) | One (or a pair) |
| Crystal Red Shrimp | ~3 cm | 19 L (5 gal) | One (or a pair) |
| Denison Barb | ~11 cm | 243 L (64 gal) | Shoal of 6+ |
| Discus | ~15 cm | 284 L (75 gal) | Shoal of 5+ |
| Dwarf Chain Loach | ~6 cm | 72 L (19 gal) | Shoal of 5+ |
| Dwarf Gourami | ~9 cm | 55 L (15 gal) | One (or a pair) |
| Dwarf Neon Rainbowfish | ~8 cm | 54 L (14 gal) | Shoal of 6+ |
| Electric Blue Acara | ~15 cm | 108 L (29 gal) | One (or a pair) |
| Electric Yellow Lab | ~10 cm | 154 L (41 gal) | Shoal of 4+ |
| Ember Tetra | ~2 cm | 30 L (8 gal) | Shoal of 8+ |
| Emperor Tetra | ~5 cm | 76 L (20 gal) | Shoal of 6+ |
| Endler's Livebearer | ~3 cm | 20 L (5 gal) | Shoal of 3+ |
| Fancy Goldfish | ~18 cm | 75 L (20 gal) | One (or a pair) |
| Firemouth Cichlid | ~12 cm | 108 L (29 gal) | One (or a pair) |
| German Blue Ram | ~5 cm | 55 L (15 gal) | One (or a pair) |
| Ghost Shrimp | ~5 cm | 19 L (5 gal) | Shoal of 6+ |
| Giant Danio | ~12 cm | 114 L (30 gal) | Shoal of 6+ |
| Glass Catfish | ~8 cm | 113 L (30 gal) | Shoal of 6+ |
| Glowlight Danio | ~3 cm | 60 L (16 gal) | Shoal of 8+ |
| Glowlight Tetra | ~4 cm | 68 L (18 gal) | Shoal of 6+ |
| Guppy | ~6 cm | 19 L (5 gal) | Shoal of 3+ |
| Harlequin Rasbora | ~4.5 cm | 40 L (11 gal) | Shoal of 8+ |
| Hillstream Loach | ~6.5 cm | 68 L (18 gal) | Shoal of 6+ |
| Honey Gourami | ~5.5 cm | 40 L (11 gal) | One (or a pair) |
| Julii Cory | ~6 cm | 75 L (20 gal) | Shoal of 6+ |
| Keyhole Cichlid | ~12 cm | 150 L (40 gal) | One (or a pair) |
| Kribensis | ~10 cm | 71 L (19 gal) | Shoal of 2+ |
| Kuhli Loach | ~10 cm | 55 L (15 gal) | Shoal of 4+ |
| Lambchop Rasbora | ~4 cm | 54 L (14 gal) | Shoal of 8+ |
| Lemon Tetra | ~5 cm | 75 L (20 gal) | Shoal of 8+ |
| Madagascar Rainbowfish | ~10 cm | 120 L (32 gal) | Shoal of 6+ |
| Molly | ~10 cm | 75 L (20 gal) | Shoal of 3+ |
| Mystery Snail | ~5 cm | 40 L (11 gal) | One (or a pair) |
| Neon Tetra | ~3 cm | 40 L (11 gal) | Shoal of 6+ |
| Nerite Snail | ~3 cm | 20 L (5 gal) | One (or a pair) |
| Odessa Barb | ~5 cm | 72 L (19 gal) | Shoal of 8+ |
| Oscar | ~35 cm | 540 L (143 gal) | One (or a pair) |
| Otocinclus | ~3.5 cm | 40 L (11 gal) | Shoal of 6+ |
| Panda Cory | ~5 cm | 41 L (11 gal) | Shoal of 6+ |
| Panda Garra | ~9 cm | 90 L (24 gal) | One (or a pair) |
| Paradise Fish | ~8 cm | 72 L (19 gal) | One (or a pair) |
| Pearl Danio | ~5.5 cm | 81 L (21 gal) | Shoal of 8+ |
| Pearl Gourami | ~12 cm | 75 L (20 gal) | One (or a pair) |
| Pictus Catfish | ~13 cm | 240 L (63 gal) | Shoal of 6+ |
| Platy | ~5 cm | 40 L (11 gal) | Shoal of 3+ |
| Pygmy Cory | ~3 cm | 41 L (11 gal) | Shoal of 6+ |
| Rabbit Snail | ~8 cm | 38 L (10 gal) | One (or a pair) |
| Ramshorn Snail | ~2 cm | 8 L (2 gal) | One (or a pair) |
| Rosy Barb | ~10 cm | 90 L (24 gal) | Shoal of 8+ |
| Rosy Loach | ~3 cm | 40 L (11 gal) | Shoal of 8+ |
| Rubber Lip Pleco | ~13 cm | 113 L (30 gal) | One (or a pair) |
| Rummynose Tetra | ~5 cm | 60 L (16 gal) | Shoal of 8+ |
| Salt & Pepper Cory | ~3.5 cm | 54 L (14 gal) | Shoal of 6+ |
| Scissortail Rasbora | ~13 cm | 114 L (30 gal) | Shoal of 6+ |
| Serpae Tetra | ~4 cm | 72 L (19 gal) | Shoal of 12+ |
| Severum | ~20 cm | 284 L (75 gal) | One (or a pair) |
| Shell-Dweller (Multi) | ~4.5 cm | 40 L (11 gal) | Shoal of 6+ |
| Siamese Algae Eater | ~15 cm | 304 L (80 gal) | Shoal of 6+ |
| Sparkling Gourami | ~4 cm | 41 L (11 gal) | Shoal of 2+ |
| Sterbai Cory | ~6.5 cm | 41 L (11 gal) | Shoal of 6+ |
| Swordtail | ~14 cm | 90 L (24 gal) | Shoal of 3+ |
| Threadfin Rainbowfish | ~4 cm | 54 L (14 gal) | Shoal of 6+ |
| Three-spot Gourami | ~15 cm | 81 L (21 gal) | One (or a pair) |
| Tiger Barb | ~6 cm | 72 L (19 gal) | Shoal of 8+ |
| Weather Loach | ~28 cm | 243 L (64 gal) | One (or a pair) |
| White Cloud Minnow | ~4 cm | 40 L (11 gal) | Shoal of 6+ |
| X-Ray Tetra | ~5 cm | 54 L (14 gal) | Shoal of 6+ |
| Yoyo Loach | ~16 cm | 243 L (64 gal) | Shoal of 5+ |
| Zebra Danio | ~5 cm | 60 L (16 gal) | Shoal of 6+ |
| Zebra Loach | ~9 cm | 108 L (29 gal) | Shoal of 5+ |
Minimums are for the first fish / a small group; heavy-waste fish like goldfish need more per extra fish. Real capacity depends on filtration and your nitrate test, not litres alone.
How many fish can my tank hold?
How many fish can I put in my aquarium?
Far fewer than the old "one inch of fish per gallon" rule suggests — that rule ignores shape, waste load and swimming needs, so don't use it. Instead, check each fish against its cited minimum tank and group size, plan for the ADULT size (not the juvenile in the shop), and let your nitrate test set the real ceiling. Enter your tank and wish-list above for an honest, per-fish read.
How many fish in a 5-gallon (19-litre) tank?
Realistically one small centrepiece plus a cleanup crew — a single betta, or a small colony of cherry shrimp and a snail. A 5-gallon is too small for a shoaling community: most schooling fish need 6+ of their kind and a 40-litre-plus tank. Bigger is easier to keep stable, so a 10–20 gallon is a kinder first tank.
How many fish in a 10-gallon (38-litre) tank?
Room for one small shoal of nano fish — for example 6–8 ember tetras, chili rasboras or celestial pearl danios — or a single betta with a few snails/shrimp. Keep to one shoaling species rather than a few of several, cycle the tank first, and don't add goldfish, cichlids or larger tetras (they need much more water).
How many fish in a 20-gallon (75-litre) tank?
Enough for a small community: a shoal of 6–8 small tetras or rasboras, a small centrepiece (a honey gourami or a betta), and a bottom cleanup crew (a group of pygmy/panda cories or shrimp and snails). Add stock gradually after cycling, and test nitrate — filtration and planting shift the real number.
How many neon tetras can I keep?
Neon tetras are shoaling fish — keep at least 6, and they're happiest in a group of 10+. Six need about a 40-litre (10-gallon) tank as a minimum; a 75-litre (20-gallon) comfortably holds a proper shoal of 10–12 with room for a small centrepiece. Never keep one or two alone — an under-grouped shoaler stays stressed.