# Aquarium Volume Calculator

> Computes the water volume of a rectangular fish tank from its internal length, width and height (cm or inches), the weight of that water (fresh or marine), a float-glass side-pane thickness estimate by Stilwell's method, and the '1 inch of fish per gallon' stocking heuristic.

- Calculator id: `aquarium-volume` · Category: Everyday Life (`everyday`) · Tool name: `calculate_aquarium_volume`
- Canonical page: https://tttkmbb.com/everyday/aquarium-volume · This document: https://tttkmbb.com/everyday/aquarium-volume.md · JSON definition: https://tttkmbb.com/everyday/aquarium-volume.json

## Purpose

Computes the water volume of a rectangular fish tank from its internal length, width and height (cm or inches), the weight of that water (fresh or marine), a float-glass side-pane thickness estimate by Stilwell's method, and the '1 inch of fish per gallon' stocking heuristic.

**Use when:** You are planning or filling a rectangular aquarium and need its capacity, the load on a stand or floor, a glass-thickness ballpark or a rough stocking limit.

**Do not use when:** The tank is bow-front, cylindrical or hexagonal (compute the footprint area separately), or you need a swimming-pool volume (use pool-volume).

## Input

| Parameter | Type | Unit | Required | Description |
| --- | --- | --- | --- | --- |
| `length` | number |  | required | Internal length of the tank. (> 0, max 2000) |
| `width` | number |  | required | Internal width. (> 0, max 2000) |
| `height` | number |  | required | Internal height (water height when full). (> 0, max 2000) |
| `unit` | enum: cm \| in |  | optional, default "cm" | Unit of the three dimensions. |
| `fill_percent` | number | % | optional, default 100 | Water height as a percentage of the tank height (allow for the air gap and substrate). (min 10, max 100) |

## Output

| Field | Type | Unit | Description |
| --- | --- | --- | --- |
| `volume_liters` | number | L | length × width × water height. |
| `volume_gallons_us` | number | US gal | Same volume in US gallons (3.7854 L). |
| `volume_gallons_uk` | number | UK gal | Same volume in imperial gallons (4.5461 L). |
| `water_weight_kg` | number | kg | Volume × 0.998 kg/L (fresh water at 20 °C), excluding glass, substrate and rock. |
| `seawater_weight_kg` | number | kg | Volume × 1.025 kg/L for marine tanks. |
| `glass_thickness_estimate_mm` | number | mm | Side-pane float glass thickness from t = √(β × H³ × 0.00001 / 5.05) with safety factor 3.8 (H = water height in mm). |
| `recommended_glass_mm` | integer | mm | Next standard sheet thickness (4, 5, 6, 8, 10, 12, 15, 19 mm) at or above the estimate. |
| `stocking_inches_of_fish` | number | inches of fish | Total adult length of small fish by the 1 inch per US gallon heuristic (rough guide only). |

## Formula

`water_height = height × fill_percent / 100; V = length × width × water_height (cm³ / 1000 = L; in³ × 0.016387 = L); US gal = L / 3.785411784; UK gal = L / 4.54609; glass t_mm = √(β × H_mm³ × 0.00001 / 5.05), β by length/height ratio: 0.5 → 0.2419, 1 → 0.294, 1.5 → 0.325, 2 → 0.3415, 2.5 → 0.35, 3 → 0.37 (interpolated, clamped); stocking = US gallons × 1 inch`

The glass formula is Warren Stilwell's method for a side pane supported on three edges: allowable stress 5.05 N/mm² (19.2 N/mm² tensile strength of annealed glass ÷ safety factor 3.8) under hydrostatic load. The 1-inch-per-gallon rule ignores fish body mass, activity and filtration and overstocks tanks with fish over about 3 inches; use it only as a first sanity check.

## Data Sources

- Aquarium World – Calculating glass thickness for aquariums (Stilwell method, β/α tables) — https://aquariumworld.nz/forums/fish/articles-guides/technical-diy/calculating-glass-thickness-for-aquariums-r23/ (reference, retrieved 2026-09-24)
- Fishkeeping – stocking rules of thumb (Wikipedia) — https://en.wikipedia.org/wiki/Fishkeeping (reference, retrieved 2026-09-24)
- Gallon – US and imperial definitions (Wikipedia) — https://en.wikipedia.org/wiki/Gallon (reference, retrieved 2026-09-24)

Data freshness: `static`. Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output.

## API

- `GET https://tttkmbb.com/api/v1/calculate/aquarium-volume?length=…&width=…&height=…`
- `POST https://tttkmbb.com/api/v1/calculate/aquarium-volume` with JSON body `{"inputs": {…}}`
- Response: unified envelope (`success`, `request`, `result.values`, `result.units`, `sources`, `freshness`, `timestamp`, `next_actions`, `links`); see https://tttkmbb.com/docs/response-format.md
- Schema: https://tttkmbb.com/api/v1/calculators/aquarium-volume · OpenAPI operationId `calculate_aquarium_volume` in https://tttkmbb.com/openapi.json
- Authentication: none. Rate limit: fair use, see https://tttkmbb.com/docs/rate-limits.md.

## MCP

- Server: `https://tttkmbb.com/mcp` (Streamable HTTP, JSON-RPC 2.0, no auth)
- Tool:  `run_calculator` with `{"calculator_id": "aquarium-volume", "inputs": {…}}`

## Example

- 100 × 40 × 50 cm tank: inputs `{"length":100,"width":40,"height":50,"unit":"cm"}` → `{"volume_liters":200,"volume_gallons_us":52.8,"volume_gallons_uk":44,"water_weight_kg":199.6,"seawater_weight_kg":205,"glass_thickness_estimate_mm":9.2,"recommended_glass_mm":10,"stocking_inches_of_fish":52.8}`
- 48 × 13 × 21 in ('55 gallon'): inputs `{"length":48,"width":13,"height":21,"unit":"in"}` → `{"volume_liters":214.7,"volume_gallons_us":56.7,"volume_gallons_uk":47.2,"water_weight_kg":214.3,"glass_thickness_estimate_mm":10.2,"recommended_glass_mm":12}`

```
GET https://tttkmbb.com/api/v1/calculate/aquarium-volume?length=100&width=40&height=50&unit=cm
```

## Limitations

The tank is bow-front, cylindrical or hexagonal (compute the footprint area separately), or you need a swimming-pool volume (use pool-volume). The glass formula is Warren Stilwell's method for a side pane supported on three edges: allowable stress 5.05 N/mm² (19.2 N/mm² tensile strength of annealed glass ÷ safety factor 3.8) under hydrostatic load. The 1-inch-per-gallon rule ignores fish body mass, activity and filtration and overstocks tanks with fish over about 3 inches; use it only as a first sanity check. All values are computed from the formula above; no measurement or live data is involved.

## FAQ

**Why is my '55 gallon' tank only 52 gallons here?**

Trade names use nominal external sizes; internal dimensions, the air gap and substrate reduce real water volume by 10–15%. Enter internal measurements and a fill_percent below 100 for the actual amount.

**Can I rely on the glass thickness estimate?**

It is a ballpark for annealed float glass panes with a rim and no bracing; manufacturers often use thinner glass with braces and thicker glass for tanks over 60 cm high. Check with the glass supplier or a dedicated calculator before building.

## Related

- [Pool Volume Calculator](https://tttkmbb.com/everyday/pool-volume.md) — Volume and chlorine dose for swimming pools.
- [Rectangular Prism Calculator](https://tttkmbb.com/geometry/rectangular-prism.md) — Plain box volume and surface area.
- [Volume Converter](https://tttkmbb.com/conversion/volume.md) — Convert litres, gallons and cubic metres.