COGO Survey

Survey unit converter

Type one value and see it in every survey unit at once, on the international or the US survey foot.

Convert
Foot used for chains, rods, miles and acres

Use US survey for older deeds, plats and many NAD 83 state plane coordinates.

Exact factors used

1 international foot = 0.3048 m (exact) 1 US survey foot = 1200 ÷ 3937 m (exact) 1 chain = 66 ft = 100 links = 4 rods 1 mile = 5,280 ft = 80 chains 1 Texas vara = 33⅓ in (36 varas = 100 ft) 1 Mexican vara = 0.838 m 1 acre = 43,560 sq ft = 10 sq chains 1 hectare = 10,000 m²

Chains, links, rods, miles, varas and acres are defined in feet, so their metric size depends on which foot is meant. The switch above sets that. The two named foot units and the metric units never change.

Worked example

An old deed calls a line 12 chains 50 links. That is 12.50 chains × 66 = 825 ft. On the US survey foot that is 825 × 1200 ÷ 3937 = 251.4605 m; on the international foot it is 825 × 0.3048 = 251.4600 m. The half-millimetre gap is the 2 ppm difference between the two feet.

Units covered

  • Length: metres, kilometres, international feet, us survey feet, inches, yards, statute miles, chains (gunter), links, rods (poles, perches), texas varas, mexican varas.
  • Area: square metres, hectares, square kilometres, square international feet, square us survey feet, acres, square miles, square chains.

Questions

What is the difference between the US survey foot and the international foot?

The international foot is exactly 0.3048 m. The US survey foot is exactly 1200/3937 m, about 0.3048006 m. The difference is 2 parts per million: about 0.01 ft in a mile, but several feet on state plane coordinates in the millions.

Which foot should I use?

The US survey foot was officially retired at the end of 2022, and new work is meant to use the international foot. Older deeds, plats and NAD 83 state plane coordinates in many states are in US survey feet, so match the record you are working from.

How long is a chain, a link and a rod?

A Gunter's chain is 66 feet and has 100 links, so a link is 0.66 ft (7.92 inches). A rod, pole or perch is 16.5 feet, a quarter of a chain. Ten square chains make one acre.

How long is a vara?

It depends on where the grant was made. The Texas vara is 33⅓ inches (36 varas = 100 feet). The Mexican vara used here is 0.838 m. California and other regions used slightly different lengths, so check the local standard.

How many square feet are in an acre?

43,560 square feet, or 10 square chains. On the international foot an acre is 4,046.856 m²; on the US survey foot it is about 4,046.873 m².