What Is a Rod?
A rod (abbreviated rd) is an old English unit of length equal to 16.5 feet, or 5.5 yards, which is exactly 5.0292 meters. The same length was also called a pole or a perch, and the three names were used interchangeably in different regions and trades. Four rods make a chain, 40 rods make a furlong and 320 rods make a mile. NIST Handbook 44 lists the rod with its exact metric value among the US customary units of length.
The rod began as a real pole, likely the goad used to drive an ox team, and its length varied from place to place before it was standardized. A famous illustration in a 1535 German book by Jakob Köbel shows how a town could set its own rod: sixteen men leaving church line up their left feet, and the total length is the rod. The English settled on 16.5 feet, and the 1593 statute that defined the mile wrote that length into law.
What Is a Mile?
The statute mile is 320 rods. The 1593 Act of Parliament under Elizabeth I defined it from the bottom up: a pole of sixteen and a half feet, 40 poles to the furlong, and 8 furlongs to the mile. That arithmetic gives 5,280 feet, a number that replaced the Roman mile of mille passus, a thousand paces, or about 5,000 feet.
In 1959 the International Yard and Pound Agreement fixed the yard at 0.9144 m, making the international mile exactly 1,609.344 meters and the rod exactly 5.5 yards of that length.
Old Surveying Units in Land Deeds
In colonial America, especially New England, property was often described in rods long before chains became common. Deeds for farms, town lots and roads might read “running easterly by the highway forty rods to a heap of stones”, with boundaries set by walls, trees and stakes. Land area was given in acres, rods and perches, where a square rod (square perch) of 272.25 square feet was the small unit and 160 square rods made an acre.
| Distance | Rods (rd) | Miles (mi) |
|---|---|---|
| One rod (about a canoe length) | 1 | 0.003125 |
| One chain | 4 | 0.0125 |
| One furlong | 40 | 0.125 |
| 100-rod portage | 100 | 0.3125 |
| Half mile | 160 | 0.5 |
| One mile | 320 | 1 |
| Two miles | 640 | 2 |
Rods also set the width of old roads. Many New England town roads were laid out “two rods wide”, 33 feet or 10.06 meters between the stone walls on either side, and those widths still define the legal road line in some places. Fences, ditches and hedges were sold and built by the rod too.
The unit is very much alive in canoe country. Portages in the Boundary Waters Canoe Area Wilderness of Minnesota and neighboring Quetico Provincial Park in Ontario are measured in rods, a convenient choice because one rod is roughly the length of a canoe. A 200-rod portage is 0.625 miles, or 3,300 feet, a distance paddlers often walk twice: once with the canoe and once with the packs.
The rod is also the hidden unit behind British allotment gardens. A traditional full-size allotment plot is 10 square rods, or “10 poles”, about 253 square meters, a size said to be enough to feed a family for a year. Many councils still let plots by the pole, and half-plots of 5 poles are common.
Older English and Irish records used the perch for land area as well: an area written as “2 acres, 1 rood, 20 perches” combines acres, roods (a quarter acre, or 40 square perches) and square perches. Converting such a figure needs the rod twice over, since one square perch is one rod by one rod.
How Many Rods in a Mile?
There are exactly 320 rods in a mile, so to convert miles to rods you multiply by 320. The number follows from the chain: 80 chains of 4 rods each. For area it squares, so a square mile is 320 × 320 = 102,400 square rods, which divided by 160 square rods per acre gives the familiar 640 acres. A quarter mile is 80 rods, a kilometer is 198.8 rods, and a 5K is 994 rods.