# How do I convert acres to hectares?

Converts acres (ac) to hectares (ha) and back, with the exact unit definitions.

- Page: https://www.acalculator.org/convert/acres-to-hectares
- JSON spec: https://www.acalculator.org/convert/acres-to-hectares.json
- Version: c48909e58850

## Default answer

Example with the default inputs (Acres (ac) 1): 1 ac = 0.404686 ha.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| value | Acres (ac) | The amount in acres to convert. |
| result | Hectares (ha) | The same amount in hectares. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| value | Acres (ac) | The amount in acres to convert. |
| result | Hectares (ha) | The amount in hectares. |

## Method

ha = ac × 0.40468564224

## Assumptions

- 1 acre = 0.40468564224 hectares, from 1 acre = 43,560 square feet of the international foot (NIST).
- Exact on the typed decimals: at most 6 decimal places (6 significant digits below 0.0001), rounded half up; an answer of 1 billion or more shows at most 15 significant digits.

## Worked examples

1. value = 1 gives result = 0.404686. Source: Exact unit definitions in NIST SP 811 (2008), Appendix B.8.
2. value = 100 gives result = 40.468564. Source: Exact unit definitions in NIST SP 811 (2008), Appendix B.8.
3. result = 100 gives value = 247.105381. Source: Exact unit definitions in NIST SP 811 (2008), Appendix B.8.

## FAQ

### How many hectares are in an acre?

1 acre is 0.404686 hectares, from the exact unit definitions (NIST).

### How do I convert acres to hectares?

Multiply by 0.404686: ha = ac × 0.40468564224. For example, 1 ac × 0.404686 = 0.404686 ha.

### How do I convert hectares back to acres?

Multiply by 2.471054, or type the hectares into the second box and the converter works it out. 1 hectare is 2.471054 acres.

### Why is an acre 0.40468564224 ha?

An acre is 43,560 square feet. With the international foot of 0.3048 m that is 4,046.8564224 m² exactly (NIST), and a hectare is 10,000 m², so 1 acre is 0.40468564224 ha.

### What about the survey acre?

Older US land records may use the survey foot, which makes an acre about 4,046.873 m², 4 parts per million more. NIST made the survey foot obsolete from January 1, 2023; this page uses the international acre.

### What is 100 acres in hectares?

40.468564 ha: 100 × 0.40468564224.

## Sources

- NIST, U.S. Survey Foot: Revised Unit Conversion Factors: 1 acre = 43,560 ft² = 4,046.856 422 4 m² and 1 mile = 5,280 ft = 1,609.344 m, exact with the international foot, retrieved 2026-10-18. https://www.nist.gov/pml/us-surveyfoot/revised-unit-conversion-factors
- NIST SP 811 (2008), Guide for the Use of the International System of Units, Appendix B.8: Factors for Units Listed Alphabetically (bold factors are exact), retrieved 2026-10-18. https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b8