Aquarium Stocking Calculator for Fish and Filter Load
Use this aquarium stocking calculator to check tank dimensions, filter turnover, adult fish size, schooling needs, and bioload warnings before you buy fish. Core stocking and filter checks are free - go Pro for stocking modes, extra bioload buffers, fish-count scenarios, and a copyable buying note.
Balanced load. Add fish slowly and keep testing ammonia and nitrate.
16 in of adult fish against 21.5 in of planning capacity.
Flow is in a common community range.
Group size meets the selected minimum.
No extra bioload warning for these inputs.
Free uses the balanced community-tank estimate. Pro unlocks conservative/heavy modes and an extra bioload buffer.
Pro unlocks stocking modes, extra bioload, fish-count scenarios, and a copyable buying note.
Unlock with ProPro unlocks stocking modes, extra bioload, fish-count scenarios, and a copyable buying note.
Unlock with ProFree to use. Pro when you need more.
One oftenoriginal Pro membership unlocks the pro features on every tool.
Free
$0- ✓Tank volume from length, width, and height
- ✓Filter turnover per hour from GPH
- ✓Adult fish size and fish-count load estimate
- ✓Schooling minimum warning
- ✓Bioload and filter warnings
- ✓No sign-up required
oftenoriginal Pro
$9/month- ✓Everything in Aquarium Stocking & Filter Load Calculator, unlocked
- ✓Conservative, balanced, and heavy stocking modes
- ✓Extra bioload buffer for messy species
- ✓Fish-count scenario table
- ✓Copyable buying note for store visits
Aquarium Stocking & Filter Load Calculator — frequently asked questions
How does this aquarium stocking calculator work?+
It estimates usable tank volume from dimensions, compares filter flow against the tank volume, then checks the planned group by adult fish size, fish count, schooling minimum, and selected bioload assumptions.
Does the calculator use adult fish size?+
Yes. Stocking is based on adult size, not the size of juvenile fish in the store. That helps avoid buying fish that will outgrow the tank or overload filtration later.
What does Pro add for aquarium stocking?+
Pro unlocks conservative and heavy stocking modes, an extra bioload buffer for messy species, fish-count scenario rows, and a copyable note you can take to the store.
Is my aquarium plan sent to a server?+
No. Tank dimensions, filter flow, fish counts, adult sizes, and stocking warnings are calculated entirely in your browser.
Related tools
More free tools from the oftenoriginal toolbox — no sign-up required.
Get new free tools monthly
We ship a new free tool nearly every day. Get the best of the month in one short email.