turf.length
What is turf.length?
turf.length takes a GeoJSON LineString, MultiLineString, or a Feature/FeatureCollection containing them and returns the total length as a number. It walks every segment and sums haversine distances between consecutive vertices — the same formula turf.distance uses.
turf.length(geojson, options?) → numberOptions include:
units—'kilometers'(default),'meters','miles','nauticalmiles','radians','degrees'
When would you use turf.length?
Use turf.length to display the length of a user-drawn route on a MapLibre map, compute trail mileage for a hiking app, or aggregate network length by road class in a Node.js pipeline. It pairs naturally with turf.along when you want to chunk a route, place mileposts, or animate along the line.
For polygons you want perimeter of, convert with turf.polygonToLine first and then call turf.length. For point-to-line distance, use turf.pointToLineDistance.
import length from '@turf/length';FAQs
Does it include every vertex or just endpoints?
Every vertex. turf.length walks each segment of the line and sums haversine distances, so densely digitised curves produce more accurate real-world length than coarse polylines.
How do I install just length?
npm install @turf/length. It depends on @turf/distance and @turf/meta and is very small.
Is a FeatureCollection supported?
Yes. turf.length accepts any GeoJSON container and sums the lengths of all LineString and MultiLineString parts it finds. Non-line features are ignored.
Why is my measured length shorter than what Google Maps says?
Usually because the input line is less densely digitised — haversine sums straight-line chords between vertices, so a polyline with few points in a curve underestimates a smooth real-world path. Densify the line (e.g. via turf.lineChunk) if you need closer agreement.
