FREE FIELD CALCULATOR
US survey foot converter
Check the difference between legacy US survey feet, international feet and metres before mixing data.
What you’ll need
- The unit definition from the file or project: “feet” alone isn’t enough
- The unit you’re converting from, and the one you need
- One value to check, with its coordinate and elevation reference
Try it with these numbers
- Choose US survey foot (legacy) in From and International foot in To.
- Enter 1000000 and calculate. Expect about 1,000,002.000004 international feet.
- Swap the source and destination units and enter 1000000 again. Expect 999,998 US survey feet.
- Compare those unit definitions with the file and project control before importing anything. Do not use this numeric check to relabel an entire coordinate system.
Reading your result
The number is the same distance expressed in another unit. The roughly two-foot difference at a million-foot coordinate value shows why the foot definition matters.
Extra displayed decimal places are useful here, unlike an order for dirt. They show the small unit difference; they do not improve the accuracy of the original survey.
Where this goes wrong on site
- “Upgrading” Wisconsin county coordinates to international feet. The Wisconsin State Cartographer’s Office advises keeping the US survey foot with NAD 83 systems such as WISCRS. The international foot comes with SPCS2022 and the modernized national reference system.
- Treating the retirement as a change to old files. NIST and NGS retired the US survey foot at the end of 2022, but records made in survey feet are still in survey feet. Check each file’s definition.
- Calling a 2 ppm difference too small to matter. At a 500,000-foot coordinate the two feet differ by 1 ft, and at 1,000,000 by 2 ft.
- Changing a unit label without converting the numbers.
- Mistaking a unit difference for a datum shift, or assuming conversion puts county, State Plane and local ground coordinates on the same system.
Sources: Wisconsin State Cartographer’s Office · NIST: U.S. survey foot
How the math works
International foot = 0.3048 metre exactly. US survey foot = 1200/3937 metre exactly. Output = input × metres per source unit ÷ metres per destination unit. NIST unit definitions and legacy guidance.
Keep the number with the job
Calculate above, then download a Letter or A4 PDF, copy the result or share it from your phone. The result sheet keeps your inputs and assumptions. Changing an input means you need to calculate again before exporting.
Open the private field workspace for saved jobs and reports across your phone and computer, or read the free-calculator guide. Tell Jesse what would make this easier on your job.
Useful on your job?
Share this free calculator with someone who could use it, or tell Jesse what needs improving.
Shares the tool link only, without your measurements. https://driftlesssolutions.us/tools/survey-foot/