---
title: "Aquarium volume and stocking — free, runs in your browser"
description: "Tank volume from its dimensions, with the real volume after substrate and displacement. Free, no sign-up, and nothing you enter leaves your browser."
url: https://atoneplace.net/tools/aquarium-volume-calculator/
site: "At One Place"
---

# Aquarium volume and stocking

Tank volume from its dimensions, with the real volume after substrate and displacement.

## How it works

Calculates a tank’s volume from its internal dimensions, in litres and both gallon measures, and estimates the actual water volume once substrate and hardscape are accounted for.

The number that matters is not the one on the box. A tank sold as 200 litres holds noticeably less water in practice: substrate takes 10 to 15%, rock and wood take more, and the water line sits below the rim. Real water volume is typically 80 to 90% of nominal, and every dose calculation — medication, fertiliser, water conditioner — should use the real figure. Dosing a planted tank by its box rating consistently overdoses it.

Weight is the part people underestimate. Water alone is 1 kg per litre, so a 200-litre tank with substrate and rock is comfortably over 250 kg concentrated on a small footprint. That is beyond what many domestic floors carry safely without checking the joist direction.

The old inch-per-gallon stocking rule is not used here, because it is unreliable — it scales fish by length while waste production scales closer to mass, so it badly under-rates large-bodied fish. Filtration, surface area and species behaviour matter more.

> This tool runs entirely in your browser. Nothing you enter is sent to a server, logged or stored, and the page keeps working with the network disconnected.

## Common questions

### How much water does my tank actually hold?

Usually 80–90% of its nominal rating once substrate, hardscape and the gap below the rim are accounted for. Use the real figure for dosing.

### How much does a full aquarium weigh?

About 1 kg per litre of water, plus substrate and rock. A 200-litre tank is comfortably over 250 kg on a small footprint.

### Is the inch-per-gallon rule reliable?

No. It scales fish by length while waste scales closer to mass, so it badly under-rates large-bodied fish. Filtration and species behaviour matter more.

## Related pages

- [Percentage calculator](https://atoneplace.net/tools/percentage-calculator/)
- [Loan and EMI calculator](https://atoneplace.net/tools/loan-calculator/)
- [BMI calculator](https://atoneplace.net/tools/bmi-calculator/)
- [Tip calculator](https://atoneplace.net/tools/tip-calculator/)
- [Age calculator](https://atoneplace.net/tools/age-calculator/)
- [Paint calculator](https://atoneplace.net/tools/paint-calculator/)
- [Compound interest calculator](https://atoneplace.net/tools/compound-interest-calculator/)
- [Calorie and BMR calculator](https://atoneplace.net/tools/calorie-calculator/)
- [Dog age calculator](https://atoneplace.net/tools/dog-age-calculator/)
- [Discount calculator](https://atoneplace.net/tools/discount-calculator/)

## Sources

- Typical range compiled from manufacturer specifications — At One Place (/about/)