Old Survey Units Converter: Rods, Chains, Links, Furlongs, Varas and Acres

A furlong is 660 feet: an eighth of a mile, 10 chains, 40 rods or 201.168 meters. A rod (also called a pole or a perch) is 16.5 feet, a Gunter's chain is 66 feet, and a link is one hundredth of a chain, or 7.92 inches. Those four numbers cover most older American deeds; the converter handles the rest, including acres, roods and the Spanish vara.

How to use the converter

Type the figure from your document, choose the unit it is written in, then choose the unit you want. Length and area are converted separately, because a "rod" of fence line and a "rod" of land are different things.

Chains and links are usually written as a decimal: "12.50 chains" (or "12 ch. 50 l.") means 12 chains and 50 links, so enter 12.5 chains. Mixed measures such as "46 rods 8 links", or land given in acres, roods and perches (A. R. P.), are easiest in two or three passes: convert each part and add.

The units, and where they came from

Gunter's chain and its links

Edmund Gunter, an English mathematician, described his surveyor's chain around 1620: 66 feet of iron in 100 links, with brass tags at every tenth link so the chainmen could count. Its cleverness was in marrying decimal arithmetic to the English acre. Ten square chains make an acre and 80 chains make a mile, so a surveyor could note "12.50 chains" and work out acreage later without fractions.

Railroad and highway surveyors often used a 100-foot engineer's chain instead, so check the scale bar on a twentieth-century plan before assuming 66 feet.

Rods, poles and perches

Three names, one length: 16.5 feet, which is 5.5 yards or a quarter of a chain. In my reading, "rods" turn up most in New England deeds, "perches" in Pennsylvania and "poles" in Virginia and the Carolinas, though every clerk had his own habits.

The catch is that the same words also measure area. When a deed says a lot contains "eight acres and one hundred rods," those are square rods, not a strip of land a quarter mile long. A square rod is 272.25 square feet, 160 of them make an acre, and 40 make a rood, which is a quarter acre.

Furlongs

The word comes from "furrow long," the length of a plowed furrow in an open field, and it settled at 220 yards, or 660 feet. Horse racing still uses it. A mile is 8 furlongs, 80 chains or 320 rods.

Varas

The vara is a Spanish yard that entered American records through Spanish and Mexican land grants, and its length varied from place to place. Texas settled on 33⅓ inches, which makes 108 varas equal to 100 yards. California records use a vara of 33 inches. In Texas you will meet the league, 5,000 varas square and about 4,428 acres, and the labor, 1,000 varas square and about 177 acres.

Acres

An acre is 43,560 square feet, 160 square rods or 10 square chains, and it has never had a fixed shape. A square acre is about 208.7 feet on a side. In the federal rectangular survey a section is 80 chains by 80 chains (one square mile, 640 acres), and a quarter of a quarter section is 40 acres, 20 chains square.

How it works

Every length is stored in feet (link 0.66, rod 16.5, chain 66, furlong 660, mile 5,280, Texas vara 2.7778, California vara 2.75). The tool multiplies your figure by the feet in the starting unit and divides by the feet in the target unit. Areas work the same way in square feet (square rod 272.25, square chain 4,356, rood 10,890, acre 43,560).

Meters use the international foot of exactly 0.3048 meters. The older US survey foot differs by about two parts per million, an eighth of an inch in a mile, and was retired by NIST at the start of 2023. The unit relationships follow the tables in NIST Handbook 44.

Worked example

With the default settings, the converter shows:

Now try an invented lot of the sort described in our guide to reading a 19th-century deed book: "thence N 78° E 46 rods... thence S 12° E 30 rods." Forty-six rods is 759 feet and 30 rods is 495 feet. As a true rectangle the lot holds 1,380 square rods, which is 8 acres and 100 square rods, or 8.625 acres. That matches the deed's "eight acres and one hundred rods," the kind of cross-check I try before trusting my reading of a faded figure.

Limits

The arithmetic is exact; the original measurement was not. Chains stretched, chainmen on hillsides measured along the slope, and compass bearings drifted with magnetic declination, which is why so many deeds say "more or less." The converter tells you what the numbers mean, not where the line sits on the ground.

Varas outside Texas and California, and Spanish-era documents anywhere, may use a different value, so check with the archive that holds the grant. The tool does not compute a lot's area from its bearings. For a real boundary, title or dispute, you need a licensed land surveyor.

For colonial records, the Julian and Gregorian date converter handles the other old measure that trips people up, and more on deeds and plats is under archives and local history.

Frequently asked questions

How long is a furlong?

660 feet, which is 220 yards, an eighth of a mile, 10 chains or 201.168 meters.

How many feet are in a rod?

16.5 feet. To turn rods into feet, multiply by 16.5.

How long is a chain in feet?

A Gunter's chain is 66 feet, or 100 links of 7.92 inches. To turn chains into feet, multiply by 66. An engineer's chain is 100 feet.

Are a rod, a pole and a perch the same thing?

As lengths, yes: all three are 16.5 feet. In descriptions of area, "rods" and "perches" usually mean square rods of 272.25 square feet.

How long is a vara?

33⅓ inches in Texas records and 33 inches in California records. Elsewhere it varied.