Land Measurement Units Glossary: Acres, Hectares, Chains & More

July 18, 2026

Land measurement carries more historical baggage than most unit systems still in daily use. Here’s what the core terms mean for the acreage calculator.

Acre

The standard US and UK land-area unit, legally fixed at exactly 43,560 square feet. Originally the area a team of oxen could plow in a day — a strip one chain wide by one furlong long. See acreage calculator examples for the math applied to real parcel sizes.

Hectare

The metric-system land-area unit used across most of the world, defined as a perfect 100 m × 100 m square (10,000 sq m). One hectare equals about 2.47105 acres — the figure the acreage calculator uses to convert between the two systems.

Chain

A historical surveying unit equal to 66 feet, still the basis of the acre’s definition today. One chain is also 4 rods or 100 links. Surveyors used an actual physical chain of this length — Gunter’s chain — to measure distances in the field before modern equipment existed.

Rod (Pole / Perch)

A unit equal to 16.5 feet — a quarter of a chain. The three names (rod, pole, perch) refer to the exact same length and show up interchangeably in old deeds and county assessor records, which can be confusing when reading a historical property description.

Link

A unit equal to 7.92 inches — 1/100th of a chain. Links rarely appear in modern use but still turn up in older metes-and-bounds legal descriptions, where distances were originally recorded in chains and links rather than feet.

Furlong

A unit equal to 660 feet, or 10 chains. Combined with the chain, it’s the other half of the acre’s historical definition: one chain wide by one furlong long multiplies out to exactly 43,560 sq ft.

Section

A unit of the US Public Land Survey System (PLSS) equal to 640 acres — nominally one square mile. Sections are the building block of the grid used to describe land ownership across most of the central and western United States, established by the Land Ordinance of 1785.

Township

A PLSS unit made up of 36 sections arranged in a 6×6 grid, covering roughly 36 square miles (about 23,040 acres). Township-and-range descriptions (“Township 4 North, Range 2 West”) are how the federal government originally surveyed and sold public land.

Quarter-Quarter Section

A common way to subdivide a section for sale or farming: dividing a 640-acre section in half twice yields a 40-acre quarter-quarter section — the origin of the classic “40 acres” figure seen in older land descriptions and property records.

Are

A metric unit equal to 100 square meters — 1/100th of a hectare. Rarely used on its own in the US, but it’s the base unit hectare is built from, the same way the acre is built from the square foot.

Metes and Bounds

A land-description method that defines a parcel’s boundary using compass directions and distances from a fixed starting point, rather than a rectangular grid reference. Common in the original 13 colonies and other areas surveyed before the PLSS existed — see how to measure an irregular-shaped lot for how this affects acreage calculation.

Plat

An official map showing a parcel’s boundaries, dimensions, and often its acreage, typically filed with a county recorder or assessor’s office after a formal survey. A recorded plat is the authoritative source for a parcel’s legal acreage — more reliable than any self-calculated estimate.

Survey Acre vs. International Acre

A subtle but real distinction: the US survey foot (used in historical state-plane coordinate systems) was officially deprecated by NIST and NOAA effective January 1, 2023, in favor of the standard international foot. The two differ by about 2 parts per million — negligible for a backyard lot, but occasionally relevant when reconciling old large-tract survey data against modern GPS coordinates.

Parcel

A single, legally defined unit of land under one ownership, identified by a parcel number in county assessor records. The acreage calculator computes the raw geometric area of a parcel from length and width — see common acreage mistakes for why that number can differ from a parcel’s official recorded acreage.

Understanding these terms makes old deeds, survey plats, and county records far easier to read — and explains why an “acre” has stayed exactly 43,560 sq ft since long before the metric system existed.