# US gallons to Cubic feet (gal (US) to ft³)

> Convert US gallons to cubic feet: 1 gal (US) = 0.133681 ft³. Exact conversion factor, formula, 22-row table and worked examples, with JSON API and MCP access.

- Page id: `gallons-to-cubic-feet` · Quantity: Volume (`volume`, base unit L) · Tool: `convert_units`
- Canonical page: https://tttkmbb.com/conversion/gallons-to-cubic-feet · This document: https://tttkmbb.com/conversion/gallons-to-cubic-feet.md · JSON: https://tttkmbb.com/conversion/gallons-to-cubic-feet.json (add `?value=` for a result)

## Formula

- `1 gal (US) = 0.133681 ft³`
- `cubic feet = US gallons × 0.1336805556`
- Reverse: `US gallons = cubic feet × 7.480519481`

The factor follows from the SI definitions of both units (NIST SP 811); values below are rounded to 6 significant figures, the API returns up to 12.

## Worked examples

- 5 gal (US) = 0.668403 ft³
- 12.5 gal (US) = 1.67101 ft³
- 100 gal (US) = 13.3681 ft³

## Conversion table

| US gallons (gal (US)) | Cubic feet (ft³) |
| --- | --- |
| 1 | 0.133681 |
| 2 | 0.267361 |
| 3 | 0.401042 |
| 4 | 0.534722 |
| 5 | 0.668403 |
| 6 | 0.802083 |
| 7 | 0.935764 |
| 8 | 1.06944 |
| 9 | 1.20312 |
| 10 | 1.33681 |
| 15 | 2.00521 |
| 20 | 2.67361 |
| 25 | 3.34201 |
| 30 | 4.01042 |
| 40 | 5.34722 |
| 50 | 6.68403 |
| 75 | 10.026 |
| 100 | 13.3681 |
| 200 | 26.7361 |
| 250 | 33.4201 |
| 500 | 66.8403 |
| 1000 | 133.681 |

## API

- `GET https://tttkmbb.com/api/v1/convert?value=5&from_unit=gal_us&to_unit=ft3` → unified JSON envelope with `result.values.result`, `formula`, `factor`, `sources`, `freshness`
- MCP: server `https://tttkmbb.com/mcp`, tool `convert_units` with `{"value":5,"from_unit":"gal_us","to_unit":"ft3"}`
- All volume units: https://tttkmbb.com/api/v1/units?quantity=volume · full converter: [Volume Converter](https://tttkmbb.com/conversion/volume.md)
- Authentication: none. Freshness: `static` (fixed conversion factors).

## FAQ

**How many cubic feet are in one gallon?**

1 gal (US) = 0.133681 ft³. The factor comes from the SI definitions of both units (NIST SP 811 / BIPM), so it is exact or correct to at least 10 significant figures.

**What is the formula to convert US gallons to cubic feet?**

Multiply the value in US gallons by 0.1336805556: cubic feet = US gallons × 0.1336805556. For example, 5 gal (US) = 0.668403 ft³.

**How do I convert cubic feet back to US gallons?**

Multiply by the inverse factor 7.480519481 (US gallons = cubic feet × 7.480519481), or use the cubic feet-to-US gallons page.

## Related conversions

- [Cubic feet to US gallons](https://tttkmbb.com/conversion/cubic-feet-to-gallons.md) (reverse)
- [Liters to US gallons](https://tttkmbb.com/conversion/liters-to-gallons.md)
- [US gallons to Liters](https://tttkmbb.com/conversion/gallons-to-liters.md)
- [Milliliters to US fluid ounces](https://tttkmbb.com/conversion/ml-to-fl-oz.md)
- [US fluid ounces to Milliliters](https://tttkmbb.com/conversion/fl-oz-to-ml.md)
- [Liters to Milliliters](https://tttkmbb.com/conversion/liters-to-ml.md)
- [Milliliters to Liters](https://tttkmbb.com/conversion/ml-to-liters.md)
- [US cups to Milliliters](https://tttkmbb.com/conversion/cups-to-ml.md)
- [Milliliters to US cups](https://tttkmbb.com/conversion/ml-to-cups.md)

## Data Sources

- NIST Special Publication 811 – Guide for the Use of the International System of Units (SI), Appendix B conversion factors — https://www.nist.gov/pml/special-publication-811 (standard, retrieved 2026-09-24)
- BIPM – The International System of Units (SI Brochure, 9th edition) — https://www.bipm.org/en/publications/si-brochure (standard, retrieved 2026-09-24)
- Wikipedia – Conversion of units — https://en.wikipedia.org/wiki/Conversion_of_units (reference, retrieved 2026-09-24)