Shrimp tank calculator: real water volume and how many shrimp
Enter your tank's inside dimensions to get its full volume in US gallons and litres, an estimate of the water left once substrate, rock and the gap at the top are taken out, and a cautious stocking range for the shrimp you're planning. Everything runs in your browser; nothing is sent anywhere, and the page works offline once loaded.
Common tanks:
How the calculator works
Volume. Length × width × height in inches ÷ 231 gives US gallons; in centimetres, ÷ 1,000 gives litres (1 US gallon = 3.785 litres). That's the full glass volume, which is close to the label size on most standard tanks. A bow-front adds two-thirds of the bow's extra depth across the length, and a cylinder uses π × radius² × height. Both are estimates; odd shapes and thick corner bracing shave off a little more.
Real water. Stocking should be planned from the water you actually have, not the label. We default to taking off 15%. In a standard 20 × 10 × 12 inch "10-gallon" tank, an inch of substrate and an inch of air at the top remove about 17% of the volume, and a 2-inch bed with the same gap removes 25% (about 7.8 gallons left, the worked example in our stocking guide). Substrate holds some water between the grains, and the gap matters less in taller tanks, so 15% is a middle figure. Use 10% for a thin sand cap and 25% or more for deep soil or lots of rock. For a precise number, measure the water depth (top of the substrate to the waterline) and enter that as the height with 0%.
Stocking. For shrimp that breed (cherry and bee shrimp) you get two numbers: how many to buy, and where a colony might settle on its own after months. Only the first is a shopping list. Amano, bamboo and vampire shrimp don't breed in fresh water, and ghost shrimp larvae rarely survive in a community tank, so for them the group you buy is the group you keep. Ranges over 20 are rounded to the nearest 5, because the underlying rules aren't more precise than that.
The numbers behind it
These are the figures the calculator applies to your real-water volume. Each comes from the guide linked in the last column, where you'll find the original sources.
| Species | Start with | Settled numbers (per gallon of real water) | Tank size floor | Based on |
|---|---|---|---|---|
| Cherry and other Neocaridina | About 10 (5–10 under 4 gal of water, 10–20 from 8 gal, 20–35 from 16 gal) | 5–10 mature and planted; 2–5 new, bare or with fish; dense tanks up to about 15 | 5 gal or more suggested; about 2.6 gal floor | How many cherry shrimp per gallon |
| Crystal, bee and other Caridina | About 10 or more | 3–5 mature and planted; about half that in new or bare tanks | 10 gal is a forgiving start | Stocking guide, crystal red care |
| Amano | About 3–6 per 10 gal | Doesn't breed in fresh water; numbers stay put | About 10 gal | Amano shrimp care |
| Ghost | About 3–6 in 5–10 gal | Larvae rarely survive; numbers stay roughly put | About 5 gal, 10 easier | Ghost shrimp care |
| Bamboo (fan) | About 1 per 10 gal of water (our assumption) | Limited by food in the current | About 14 gal (Practical Fishkeeping); 20 (Aquariadise) | Bamboo shrimp care |
| Vampire | 1 in 20 gal; about 1 more per extra 10 gal (our assumption) | Limited by food in the current | 20 gal for one (Aquariadise) | Vampire shrimp care |
A few cautions apply to all of them:
- Cycle first. No stocking number makes a new tank safe; ammonia and nitrite must read 0 before any shrimp go in. See how to cycle a shrimp tank.
- Footprint beats height. Shrimp graze surfaces, so a long, low tank holds more than a tall one of the same volume.
- Fish change everything. Most fish eat baby shrimp, so colonies in community tanks stay small. See cherry shrimp tank mates.
- Watch the tank, not the number. Rising nitrate, bare surfaces, smaller adults and stalled breeding are the signs to thin a colony (signs you have too many shrimp).
Setting up from scratch? Our shrimp tank setup guide covers filter, substrate, plants and water, and best substrate for shrimp explains how much substrate to buy for your tank.
FAQ
How do I work out how many gallons my tank holds?
Measure the inside length, width and height in inches, multiply them and divide by 231 for US gallons. In centimetres, divide by 1,000 for litres. That gives the full glass volume; the water you actually have is lower once substrate, rock, wood and the gap at the top are taken out.
How much water do substrate and decorations take up?
It depends on the bed depth and hardscape. In a standard 20 × 10 × 12 inch tank, an inch of substrate and an inch of air at the top take about 17% of the volume, and a 2-inch bed takes about 25%. Rock and wood add a few percent more. The calculator defaults to 15% and lets you change it.
How many cherry shrimp per gallon?
Start with about 10 in a cycled tank of 5 gallons or more. Once the colony breeds, about 5 to 10 per gallon of real water is a comfortable target for a mature, planted, shrimp-only tank, and 2 to 5 per gallon is the cautious figure for a new, bare or fish-shared tank.
How many crystal red or bee shrimp per gallon?
Plan lower than for cherry shrimp. Shrimp Tank 101 suggests about 3 to 5 per gallon for Caridina, and many keepers stock them more conservatively because they handle water swings poorly. Start with a group of about 10 or more so you get both sexes.
Can I mix species in one tank?
Yes, with care. Amano shrimp and cherry shrimp are a popular pairing, but ghost shrimp eat baby cherry shrimp. Waste adds up across every species, so plan the main colony at the cautious end of its range and count larger shrimp such as Amanos on top of it.
Why does the calculator suggest buying so few shrimp?
Cherry and bee shrimp breed, so a starting group of about 10 grows into a full colony on its own. A new tank also has little biofilm to graze. The colony range is where a tank may settle after months, not a shopping list.
Sources: stocking figures as compiled in our guides, which cite Fishkeeping World, Shrimp Tank 101, The Shrimp Farm, Cherry Shrimps UK, Aquarium Co-Op, Practical Fishkeeping, Aquariadise and Vazquez et al. (Journal of Crustacean Biology, 2017). Volume formulas, the displacement percentages, the bow-front approximation, the filter-feeder counts and all rounding are our own arithmetic and assumptions. Checked November 2026.