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FixFinder API

Convert coordinates from your own software. Same math as our coordinate converter and batch converter.

What it costs

API access is an add-on: $20 a month or $200 a year. It is not included in Pro. You need an active Pro or Team plan, plus the add-on. Team members each get their own keys.

Get a key

Sign in on the Pro page.
Tap one of the buttons above, or the one in the API keys box, and pay in Stripe's checkout.
Back on the Pro page, type a name and tap Make a key.
Copy the key right away. It starts with ffk_. We only show it once. We store a scrambled (hashed) copy, so we can't show it again. Lost it? Revoke it and make a new one.

Keep your key secret. Don't put it in a web page or a public code repo. Anyone with it can use your points.

Convert points

Send a POST to https://findrtk.com/api/v1/convert with your key in the Authorization header.

curl https://findrtk.com/api/v1/convert \
  -H "Authorization: Bearer ffk_YOUR_KEY" \
  -H "Content-Type: application/json" \
  -d '{"from":"nad83","to":"spcs:3702","points":[[40.29,-80.24,300]]}'

Answer:

{"from":"nad83","to":"spcs:3702","count":1,
 "results":[{"out":[1273971.615707687,358292.4628343668,300],
             "zone":"3702","unit":"usft","epsg":2272}],
 "usage":{"month":"2026-10","used":1,"cap":10000,"left":9999}}

Results come back in the same order you sent them. If one point fails, that result has an error instead of out, and the rest still work.

Point order

Latitude and longitude: [lat, lon] or [lat, lon, height], in decimal degrees. West is negative.
State Plane and UTM: [easting, northing] or [easting, northing, z].
The third number (height or z) is passed through unchanged.

Systems

Value	What it is	Use as
`nad83`	NAD 83 latitude and longitude (survey gear on a US RTK network)	from or to
`wgs84`	WGS 84 latitude and longitude (phones, Google Maps). We shift it into NAD 83(2011) with NGS's EPSG:8970 at epoch 2026.8, like the web tools. Good to a few inches, not survey-grade.	from only
`spcs:3702`	NAD 83 State Plane by zone number, in the state's legal unit. Add a unit to pick one: `spcs:3702:usft`, `:ift` or `:m`.	from or to
`spcs:auto`	Each point's own State Plane zone, in that state's legal unit (or add `:usft`, `:ift`, `:m`). Each result tells you its zone, unit and EPSG code.	to only
`utm:17`	NAD 83 UTM by zone number (meters, north)	from or to
`utm:auto`	Each point's own UTM zone	to only

Zone numbers are the same ones in the coordinate converter's zone list.

Check your usage

curl https://findrtk.com/api/v1/usage -H "Authorization: Bearer ffk_YOUR_KEY"

This shows points used and left this month. It doesn't count against your limits.

Limits

10,000 points per key per month. The month resets on the 1st (UTC). Need more? Email [email protected] and we can raise it.
60 requests a minute per key.
5,000 points per request, and a 1 MB body.
3 keys per account.
Every point you send counts, even one that comes back with an error.

Errors

Errors come back as JSON like {"error":"rate_limit","message":"..."}.

Status	error	What to do
400	bad_json, no_points, bad_system	Fix the request body.
401	no_key, bad_key	Send `Authorization: Bearer ffk_...` with a key that hasn't been revoked.
402	no_pro, no_addon	Your Pro or Team plan, or the API add-on, isn't active.
413	too_many_points, too_big	Split the job into requests of 5,000 points or fewer.
429	rate_limit, monthly_cap	Wait the number of seconds in the `Retry-After` header.

The fine print

These are planning numbers, not a survey. Check them in the field before you rely on them. See the terms. Questions: [email protected].