Blog · September 30, 2026
What Is an Engineer’s Chain?
An engineer’s chain is 100 feet, divided into 100 links of one foot. It is not Gunter’s chain of 66 feet. Old road, railroad, and some city notes use the 100-foot chain, and converting them as if they were 66-foot chains shrinks the line.
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Two chains, two lengths
Gunter’s chain, the one in public-land field notes and in most farm deeds, is 66 feet, and its link is 0.66 feet. The engineer’s chain, also called a Ramsden chain in some texts, is 100 feet, and its link is 1 foot. Railroad, canal, highway, and some municipal work preferred the 100-foot chain because stationing is in hundreds of feet. If a note says 4 chains and you assume 66 feet, you get 264 feet. If that note was an engineer’s chain, the call is 400 feet. The difference is large enough to put a building on the wrong side of a line. The document has to tell you which chain, by its office, its era, and its words. A railroad station equation will be in the 100-foot world. A section-line chainage in the GLO notes will be in the 66-foot world.
How the links give it away
In Gunter’s measure, 100 links equal 66 feet, so a call of 50 links is 33 feet. In engineer’s measure, 50 links is 50 feet. A note that treats a link as a foot is using the engineer’s chain or is simply talking in feet and using the word link loosely. Do not guess. Read the title of the notes, the agency, and a known distance if one is also given in feet. Mixed notes exist. A right-of-way map may use stations of 100 feet while an adjoining farm deed uses Gunter’s chains. Convert each call in its own unit. Adding them in chain units before you convert is how gaps appear on paper that were never on the ground.
What not to do with a wheel
A measuring wheel marked in feet can check your conversion arithmetic on a sketch. It cannot retrace the line, and it is not a survey. Neither is a laser measure or a phone. The county GIS measure tool returns a grid or screen distance in its own system. It will not tell you whether the 1880 notes meant 66 or 100. Platbookmapper does not convert chains. It links to the county assessment map. When the unit is unclear, stop and get the original notes rather than picking the chain that makes the tract match a tax acreage. Forcing the unit to fit the tax map makes the tax map the authority. It is not.
What to do next
- Decide which chain that document uses before you multiply.
- Use 100 feet for an engineer’s chain and 66 feet for Gunter’s chain.
- Convert links only after you know which link.
- Keep road stationing and farm chainage in separate columns.
The mix-up to avoid
Multiplying every historical chain by 66. Railroad and many engineering notes are in 100-foot chains. The 66-foot habit silently shortens those lines.
Questions people ask
Is a station the same as an engineer’s chain?
A full station is 100 feet, so it matches the length of an engineer’s chain. Station 12+50 is 1,250 feet along the centerline from the starting station. You still read the station equation on that map, because projects sometimes restart stationing.
Did city plats use the engineer’s chain?
Some did, some used feet, and some used Gunter’s chain because the surveyor came from land work. The plat legend or the notes control. There is no national rule that all city work switched in a certain year.
Find the county map
The county GIS map is the practical place to start. Find it from the Platbookmapper directory, then treat the recorded plat and deed as the documents behind the picture.
Not a survey. County GIS and tax parcel maps are assessment and planning layers. They are not a substitute for a recorded plat, deed, or licensed survey.