JoseFitani
🗺️ Area & Perimeter

Perimeter Calculator

Calculate the perimeter of a polygon by entering its vertices in lat/lng.

This page explains how the perimeter calculator works, the data and formulas behind it, and how to interpret the result. The spherical excess formula gives the exact area of a polygon on a sphere. It works for polygons of any size, from small plots to entire countries, and is accurate to within ~0.1% of the more complex ellipsoidal formula. The tool is one of 329 free, open tools on JoseFitani for maps and geography. It runs in your browser with no sign-up needed. Use the search field or click the map to drop a pin - the tool uses the spherical excess formula for area on a sphere, plus great-circle distances for perimeter and returns the result in seconds. Below you'll find a step-by-step guide, real use cases, the methodology, FAQs, and data sources.

Click on the map to add vertices. The polygon will be drawn and the area calculated in real time.

Loading map…
0 vertices

How to use this tool

1
Enter your input

Type your query, paste coordinates, or click on the map. The tool uses the spherical excess formula for area on a sphere, plus great-circle distances for perimeter to process your input locally in the browser.

2
View the result

The result appears instantly with the map showing your location. You can adjust by clicking elsewhere or searching a new place.

3
Copy or share

Click Copy to save to clipboard, or Share to send a direct link with the exact inputs.

What people use this tool for

Fencing cost estimates

Ranchers and landowners price fencing jobs by the total boundary length, not the area inside. Tracing the property line gives the perimeter in metres and feet for material quotes. Adding a few percent for gates and waste turns it into a workable budget.

Example: A cattle rancher outside Fort Worth measures a 40-hectare pasture boundary to order barbed wire, and the tool's figure beats the rough county-assessor guess.
Property boundary verification

Buyers sanity-check a deed's stated boundary length against the visible plot outline. A mismatch can flag an encroachment or a recording error before money changes hands. The traced perimeter is not a legal survey, but it is a cheap early warning.

Example: A buyer in Kochi traces a waterfront plot and finds the shoreline edge far shorter than the deed implies, prompting a surveyor visit before signing.
Garden and lawn edging

Landscapers quote edging, hedging, and border planting by linear metres around beds and lawns. Walking the outline with a phone's GPS or tracing it on the map produces the perimeter in one pass. That beats pacing it off with a tape across soft soil.

Example: A gardener in Goa measures the curved beds of a villa lawn to price stone edging per metre.
Running route design

Coaches lay out training loops of a target distance through parks and neighbourhoods. Tracing candidate loops shows the perimeter of each option in kilometres. Small adjustments to a corner tune the loop to the workout plan.

Example: A running club in Amsterdam tweaks a park loop until the traced perimeter reads exactly 5.0 kilometres for their weekly time trial.

How it's calculated

Perimeter is the sum of great-circle distances between consecutive vertices.

The calculation runs in your browser - no data is sent to our servers. Map tiles come from OpenStreetMap (ODbL license), geocoding uses Nominatim (1 request/second limit), and elevation uses the Open-Elevation API backed by SRTM data. All are free, open services.

All calculations use the WGS84 datum (EPSG:4326), the same as GPS. For other datums (NAD27, NAD83, ETRS89), a separate conversion is needed. The difference is typically under 1 metre - negligible for most uses but important for survey-grade work.

The formulas match those in professional GIS software (QGIS, ArcGIS, Global Mapper), just in a browser-friendly form. For sub-metre accuracy, use professional software with ellipsoidal calculations. Results are shown in multiple units: km and miles for distance, km²/m²/hectares/acres for area, metres and feet for elevation. Conversion factors are exact (1 mile = 1.609344 km), so the only error source is input precision.

Related tools and resources

For more tools in this category, explore the related tools listed below. Each tool includes full documentation, examples and FAQs. Explore related tools in our Area category for complementary functionality. See the Tools index for all 329 tools, or read our blog for in-depth articles on geography and maps.

Frequently asked questions

Can I close the polygon automatically?

Yes - the last point connects back to the first.

Is perimeter just the sum of straight-line distances between my points?

Essentially yes, but computed as geodesic distances on the earth's surface rather than flat-map rulers. Each segment follows the shortest path over the sphere between its two endpoints. Summing those segments gives the true ground distance of the boundary.

Why is the result longer than the straight crow-flight distance?

Because a boundary rarely runs in a straight line: every bend, corner, and curve adds length. The crow-flight distance measures the gap between the two farthest points, while the perimeter walks the whole edge. The more irregular the shape, the bigger the gap between the two figures.

How many vertices should I place?

Enough to follow the shape's bends without overdoing it. On a straight fence run, two endpoints suffice; on a winding stream boundary, drop a vertex at each visible bend. Doubling the vertices on a smooth curve converges on the true length, so add points where the boundary changes direction.

Does the tool close the polygon automatically?

Yes. The final side is measured from your last vertex back to the first, completing the loop. You do not need to repeat the starting point. If your shape is meant to be an open path, each missing side is still counted, so use a dedicated distance tool for open routes.

Which units can I see the result in?

The perimeter is shown in kilometres, metres, miles, and feet. Fencing suppliers quote in feet or metres, surveyors in metres or chains, and runners in kilometres or miles. Pick the unit your material list or race plan expects.

How accurate is a traced perimeter?

The segment math is exact for the points you place; accuracy comes down to vertex placement. Tracing a satellite image closely usually lands within a percent or two of a ground survey. On long boundaries, zoom in before placing vertices so each corner sits on the true line.

Can I measure the perimeter of a lake or island?

Yes, as long as you can see the shoreline on the map and trace it. Shorelines are fractal, so the number keeps growing as you add detail: a 50-vertex trace gives a practical working figure. For a comparable figure between two dates, trace both with similar vertex density.

Does it work offline after the page loads?

Yes. Perimeter math runs locally in the browser from the coordinates you enter. You need a connection only to load the page and, if you want one, the background map.

Data sources & methodology