Acre Types: International, US Survey, Commercial, and Builder's Acres
An acre is not always an acre. Four definitions exist, and one was quietly deprecated in 2022. Here is what each means and which one applies to your deed or listing.
Updated April 2026
International Acre
43,560 sq ft exactly
The modern global standard since the 1959 International Yard and Pound Agreement. Defined as exactly 4,046.8564224 square metres. Used in all US, UK, Canadian, and Australian real estate listings and legal descriptions written after October 2022.
- -4,046.8564224 m2 exactly
- -0.40468564224 hectares
- -1/640 of one square mile
- -Used in all modern property transactions
US Survey Acre
~43,560.174 sq ft
Based on the US survey foot (1200/3937 metres), which is slightly longer than the international foot (0.3048 m exactly). The National Geodetic Survey deprecated the US survey foot on October 1, 2022. All new federal surveys now use the international foot and international acre. Older legal descriptions referencing US federal land may still use the survey foot.
- -4,046.872609874 m2 (slightly larger)
- -Difference from international: ~3.22 sq ft per 640 acres
- -Negligible for residential lots; only matters at very large scales
- -Historical federal land records may reference this unit
Commercial Acre
~36,000 sq ft
Not a legal or SI unit. A historical US real-estate convention used in some grid-laid-out cities when subdividing a parcel into building lots. The convention "deducted" approximately 17.4% of the gross parcel area to account for streets, sidewalks, and alleys that would serve the new lots - leaving roughly 36,000 sq ft (about 82.6% of a standard acre) as the "commercial acre" of usable land.
- -Approximately 36,000 sq ft (82.6% of a standard acre)
- -No national standard - the percentage varies by city and era
- -May appear in old city deeds or subdivision plans
- -Never use it in a modern contract without defining it explicitly
Red flag: if you see "commercial acre" in a modern real estate contract or marketing brochure without a square-footage definition, always ask for clarification. The difference between 36,000 and 43,560 sq ft is 17.4% of the parcel.
Builder's Acre
~40,000 sq ft
Used informally by some US home builders and developers to describe a nominal working acre in residential subdivision math. The term is not standardised and has no legal definition. Where it appears, it typically refers to approximately 40,000 sq ft - about 92% of a standard acre. It rarely appears in legal descriptions; its natural habitat is marketing brochures and informal planning conversations.
- -Approximately 40,000 sq ft (no fixed definition)
- -Never appears in legal descriptions
- -Always confirm square footage if you see this term
Practical Implications by Scale
| Parcel Size | Intl vs Survey diff |
|---|---|
| 1 acre residential lot | 0.2 sq ft |
| 640 acres (1 section) | 3.22 sq ft |
| 10,000 acres (large ranch) | 50 sq ft |
| 1 million acres (state park) | 5,000 sq ft |
Important: The commercial acre vs standard acre difference (17.4%) is not negligible. Always confirm which definition applies when the term "commercial acre" appears in any document.
Which Acre Is in My Document?
Modern real estate listing or deed (post-2022)
International acre. 43,560 sq ft.
Pre-2022 US federal land deed or BLM plat
Likely US survey acre. Difference from international is about 0.0004% - negligible for most uses.
City zoning document or old subdivision plan
Possibly commercial acre (~36,000 sq ft). Always confirm.
Builder's brochure or residential development marketing
May be builder's acre (~40,000 sq ft). Always confirm the exact square footage.