Acres to hectares converter
1 acre is 0.404686 hectares. To convert acres to hectares, multiply the acres by 0.404686.
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40 acres =
16.1874ha
Formula: ha = ac × 0.4046856422
Show the steps
- Definition: 1 acre = 43 560 ft² = 4046.8564224 m² (international foot); 1 ha = 10 000 m² exactly
- 40 ac × 0.4046856422 = 16.1874 ha
Definitions used: 1 acre = 43 560 ft² = 4046.8564224 m² (international foot); 1 ha = 10 000 m² exactly.
Source: NIST Handbook 44 (2026), Appendix C and NIST SP 811, Appendix B.8, checked on .
How to convert acres to hectares
Multiply the value in acres by 0.4046856422. The factor follows from the definitions: 1 acre = 43 560 ft² = 4046.8564224 m² (international foot), and 1 ha = 10 000 m² exactly.
ha = ac × 0.4046856422
Worked example: 40 ac to ha
- Definition: 1 acre = 43 560 ft² = 4046.8564224 m² (international foot); 1 ha = 10 000 m² exactly
- 40 ac × 0.4046856422 = 16.1874 ha
- Answer: 40 ac = 16.1874 ha.
Acres to hectares chart
| Acres (ac) | Hectares (ha) |
|---|---|
| 0.25 | 0.101171 |
| 0.5 | 0.202343 |
| 1 | 0.404686 |
| 2 | 0.809371 |
| 2.471 | 0.999978 |
| 5 | 2.02343 |
| 10 | 4.04686 |
| 20 | 8.09371 |
| 40 | 16.1874 |
| Acres (ac) | Hectares (ha) |
|---|---|
| 50 | 20.2343 |
| 80 | 32.3749 |
| 100 | 40.4686 |
| 160 | 64.7497 |
| 250 | 101.171 |
| 320 | 129.499 |
| 500 | 202.343 |
| 640 | 258.999 |
| 1,000 | 404.686 |
Values rounded to 6 significant digits. Type any other number in the converter at the top of the page.
How big is an acre compared with a hectare?
A hectare is the larger one: 10,000 m², a square of 100 m by 100 m. An acre is 43,560 square feet, 4,046.86 m², so one hectare is 2.47105 acres, roughly two and a half.
Did the size of the acre change in 2023?
By a hair. Until the end of 2022 the US acre was tied to the U.S. survey foot and measured 4,046.872609874 m². NIST retired the survey foot (85 FR 62698), and the acre is now 4,046.8564224 m² on the international foot. The difference is 4 parts per million: about 0.016 m² per acre, or 16 m² on a 1,000-acre property. NIST keeps the survey definition for historic and legacy records.
More questions about acres and hectares
How many hectares is 1 acre?
1 acre is 0.40468564 hectares.
How many acres is 1 hectare?
1 hectare is 2.47105 acres. NIST Handbook 44 lists it as 2.471 054.
How many hectares is 100 acres?
100 acres is 40.4686 hectares.
How many acres is a square mile?
A square mile is exactly 640 acres, about 259 hectares.
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Sources and limits
- NIST Handbook 44 (2026), Appendix C
NIST Handbook 44-2026, Appendix C: General Tables of Units of Measurement.
National Institute of Standards and Technology. Edition or effective date: . Text in force when checked on .
- NIST SP 811, Appendix B.8
NIST Special Publication 811, Guide for the Use of the SI, Appendix B.8: Factors for Units Listed Alphabetically (page updated August 18, 2025).
National Institute of Standards and Technology. Edition or effective date: . Text in force when checked on .
- NIST, U.S. survey foot (85 FR 62698)
Federal Register notice of October 5, 2020 (85 FR 62698): the U.S. survey foot is superseded by the international foot from January 1, 2023.
National Institute of Standards and Technology. Edition or effective date: . Text in force when checked on .
This is a calculation aid, not an official measurement service. Results are rounded to 6 significant digits for display. For trade, engineering, medical dosing or legal documents, confirm the figure in the official source. Nothing you type leaves your browser.