Acre
An acre is a unit of land area equal to 43,560 square feet, or 160 square rods, and it has no required shape. A parcel's legal acreage is the figure carried by its recorded plat and deed, not the number a county map layer displays.
43,560 square feet, in whatever outline the ground takes
The number is fixed at 43,560 square feet. The square is not. An acre of hillside pasture can be a long strip along a fence line, a wedge between two roads or a ragged shape following a creek, and it is still exactly an acre.
Handbook 44, the weights and measures handbook published by the National Institute of Standards and Technology, puts the acre at 43,560 square feet, which is also 160 square rods, and a square mile at 640 acres. The same handbook makes the point about shape directly:
For example, an acre is not necessarily a regular shape, such as a square or rectangle.
NIST Handbook 44, Appendix C
If an acre does happen to be square, each side is about 208.71 feet. That figure is handy for picturing size and almost useless for reading a real tract, because very few rural parcels are square and a narrow acre and a square acre can hold very different amounts of usable ground. How much ground a home actually takes is a separate question, answered in how much land you need to build a house here.
One quiet change sits behind the unit itself. The handbook notes that the acre was previously defined only in terms of the U.S. survey foot, and that beginning January 1, 2023 the U.S. survey foot should be avoided except for historic and legacy applications, with the international foot taking its place. Deeds and plats recorded before that date predate the change.
The recorded plat and deed hold the acreage a county map only approximates
A tract can carry more than one acreage figure: one in the deed, one in the tax records and one on the county's online map. When they disagree, Carroll County's own map viewer says which source it treats as authoritative.
Carroll County's Web GIS asks every user to agree to its terms before entering, and those terms say its map layers and data are for general reference only and that, when researching real estate, recorded plats and deeds are the authoritative source for legal acreage and ownership. Grayson County's WebGIS is blunter about where its lines came from:
The boundaries that are depicted on this site are not certified as survey accurate, and thus they are not legally binding.
Grayson County WebGIS
So a map outline, and any acreage calculated from it, is a way to find a parcel and see roughly where it lies. In Carroll County the Commissioner of the Revenue maintains the tax identification maps and the GIS parcel layer, and the county's own pages call a parcel's number its Tax Map/Parcel ID number, the local counterpart of what other counties call a GPIN. How the plat, the parcel number and the map fit together in the record is set out in plats and GPINs in the county record.
Each of the current land listings says where its acreage figure comes from.
Rural area to a hundredth of an acre, computed from the lines
When a surveyor runs a new boundary, the acreage is computed rather than estimated. Virginia's minimum standards for land boundary surveys, 18VAC10-20-370, tell the surveyor how precisely to report it.
A boundary survey plat must show, among other items, the area of property in rural areas "to the nearest hundredth (.01) of an acre or equivalent."
That area is not measured separately from the lines. It follows from the bearings and distances around the perimeter, which is why a deed's acreage and its metes and bounds description belong together. When the acreage written in an old deed and the area computed from its calls do not match, the surveyor is the one who says which the ground supports.
Deed says one acreage and the tax card another?
Send the tax map number and the deed book and page, and Lowell will look at both figures and say how the gap bears on a sale and who can settle it. No cost, no obligation.
Got it. Thank you.
We'll be in touch shortly with an honest read.
Questions about this term
Why would the tax records show different acreage from my deed?
County map layers are reference tools. Carroll County's Web GIS says recorded plats and deeds are the authoritative source for legal acreage, and Grayson County's WebGIS says its lines began as hand drawn maps. In Carroll, the Commissioner of the Revenue keeps the tax identification maps and is the office to ask about the figure in the tax records; a land surveyor reconciles the deed with the ground.
Did the 2023 retirement of the U.S. survey foot change what an acre is?
The acre is still 43,560 square feet. What changed is the foot behind it: NIST notes the acre was previously defined only in terms of the U.S. survey foot, which since January 1, 2023 should be avoided except for historic and legacy applications. Which foot an older survey relied on is a question for the surveyor retracing it.
Where this page's facts come from
Every rule, office and figure above traces to one of these. Rules change; check the office before you act on one.
- NIST Handbook 44 (2026), Appendix C: General Tables of Units of Measurement National Institute of Standards and Technology
- Carroll County Web GIS: public access terms Carroll County, Virginia
- Grayson County WebGIS Grayson County, Virginia
- Commissioner of the Revenue Carroll County, Virginia
- 18VAC10-20-370: minimum standards and procedures for land boundary surveying practice Virginia Administrative Code