Perimeter Calculator
Draw a shape and read geodesic perimeter alongside area.
By Aryan Khan, Founder & Editor · Updated October 2026
For example, a drawn boundary of four long edges can total 10.75 km (6.68 miles) of perimeter — the fencing, edging and walking distance hiding inside one innocent-looking field.
How to use Perimeter Calculator
Draw the shape; walk its edge in numbers:
The Perimeter Calculator measures the total boundary length of a polygon you draw on the map, summing its edges geodesically. Trace the shape and read the perimeter in feet or miles — the number behind fencing estimates, edging orders and boundary walks.
- 1Draw polygon vertices.
- 2Close the shape.
- 3Read perimeter and area.
What people use Perimeter Calculator for
1. Fencing estimates
Perimeter is fence length: a 100 × 150 ft lot's 500 ft of boundary becomes ten 50-ft rolls before posts are counted. Rectangular plots shortcut through the Fence Length Calculator.
2. Edging, kerbing and borders
Garden edging, sports-field lines, parking-lot kerbs — all are sold by the metre of boundary, and all begin with this sum.
3. Boundary walks and inspections
Rangers, surveyors' assistants and parish boundary-beaters plan the walk from the perimeter: 10.75 km of boundary is a half-day's inspection, not a stroll.
4. The other half of area
Area's sibling measurement: two fields can share an acreage and differ wildly in perimeter — the long thin one costs more to fence, hedge and maintain. The Map Area Calculator gives the pair.
Worked examples
The drawn four-sided parcel from the area examples carries 10.75 km of boundary (6.68 mi) around its 6.08 km². Stretch the same area into a long strip and the perimeter balloons — shape, not size, sets the fence bill.
100 × 150 ft: perimeter 500 ft exactly — 2 × (100 + 150). Simple rectangles check the tool's arithmetic at a glance, which is why they headline the examples.
Perimeter reference points
Boundary lengths for shapes everyone pictures.
| Shape | Perimeter |
|---|---|
| 100 × 150 ft lot | 500 ft |
| Square acre (208.7 ft sides) | 834.8 ft |
| Football field (360 × 160 ft) | 1,040 ft |
| 1-mile-radius circle | 6.28 mi of circumference |
| Drawn example parcel | 10.75 km |
Circles have no edges to sum — their boundary is the circumference, 2πr; the radius tools handle that family. Polygons are this page's trade.
Mapped perimeter measures the drawn boundary, so vertex placement controls the result
A geodesic perimeter calculation adds the surface distance between consecutive polygon vertices and closes the shape. It is useful for fences, fields, site boundaries and comparing alternative outlines.
A simplified polygon can underestimate a winding real boundary, while noisy or excessive vertices can inflate length. For legal property boundaries, construction or surveying, use authoritative survey geometry rather than a hand-drawn map outline.
How to interpret the result
The most common errors come from using a correct result to answer the wrong geographic question. Keep these points in mind for Perimeter Calculator:
- When exporting polygons for reports, store the radius and unit in the feature properties (the exports here do). Future-you, reopening the file in a GIS, will otherwise have to re-derive what the circle meant.
- Decide geometric vs temporal reach before drawing anything: a 10 km circle and a 15-minute drive area answer different questions, and in car-dependent geography they barely overlap in shape. Circles for policy radii, isochrones for response promises.
Limits & appropriate use
Circles and polygons are geometric truths with semantic limits. A radius says nothing about rivers, one-way systems or response times; an area says nothing about what is inside it. The most expensive misuse is treating a geometric catchment as a service promise — which is why the isochrone tools exist as the temporal counterpart, and why the pages cross-link the two insistently. A second limit is resolution: drawn vertices capture the boundary you click, so curved shores want more clicks, and the perimeter grows (correctly) as you add them — the coastline paradox, politely present in every honest measurement tool.
Within geometry, the numbers are exact on the sphere: areas by spherical excess, boundaries by destination math, exports with their parameters embedded. The escalation ladder is short: cadastral precision needs licensed surveys; population-inside-shapes needs census blocks; drive-time promises need the routing engine. Used as the fast, auditable, shareable geometric layer that feeds those heavier instruments, this is exactly the right tool — and it says so.
- Cadastral/legal area → licensed survey with local datum practice.
- Population inside shapes → census blocks, not city-point sums.
- Response-time promises → isochrones plus operational buffers.
Data & methodology
The polygon workspace sums spherical distances between consecutive vertices, including the closing edge; it is not a road or surveyed boundary measurement.
For source details, licences and model limitations, see Data Sources and Methodology.
Key terms worth knowing
- Perimeter
- The summed great-circle length of a drawn boundary.
- Spherical cap
- The true shape of a radius circle on a globe.
Editorial guidance: MapBench explains the method and limitations so the tool can be used as a transparent reference, not as a black-box answer. For legal boundaries, safety-critical routing, surveying, engineering, regulated decisions or official statistics, verify the result with the responsible authority or a qualified professional.
Category: Radius & Area. Results are intended for everyday analysis and planning unless a page explicitly states otherwise.
Method, assumptions & limits
- This tool’s method
- The polygon workspace sums spherical distances between consecutive vertices, including the closing edge; it is not a road or surveyed boundary measurement.
- Before relying on the answer
- Check the centre, radius or drawn vertices and the selected units. A geometric footprint does not describe which roads or entrances are accessible.
- What the result cannot establish
- A radius is not a travel-time guarantee. For parcel boundaries or legal land area, use an authoritative survey.
Coverage: Worldwide. Search, basemap and external data requests may use third-party services; browser-based does not mean every operation is offline. Read the source and licence notes, calculation methodology and privacy policy. If a result looks inconsistent, report a correction with the inputs and mode used.
Frequently asked questions
Clear answers about the calculation, accuracy and appropriate use.
Same as area tool?
Same drawing engine — focused on perimeter readout.
Is a radius the same as driving distance?
No. A radius is a geometric circle around a centre point. Driving reach depends on the road network and usually has an irregular shape.
Can I use this for service-area planning?
Yes for first-pass planning. Use a drive-time or road-network tool when accessibility matters more than straight-line coverage.
Are map measurements legal survey measurements?
No. MapBench measurements are planning/reference outputs unless a page explicitly states otherwise. Use a licensed surveyor for legal boundaries.
How is the perimeter computed?
Each edge is a geodesic (great-circle) segment between consecutive vertices, and the perimeter is their sum — with the closing edge from the last vertex back to the first included.
Does the calculator close the shape automatically?
Yes — the boundary is a loop by definition. If your shape is an open path (a trail, a coastline stretch), the Trail Distance Estimator measures open lines instead.
Gates and gaps in a fence?
Subtract them after: a 500 ft boundary with two 4-ft gates needs 492 ft of fencing. The perimeter is the gross figure every net figure starts from.
Curved boundaries?
Approximate curves with more vertices — each added point tightens the sum toward the true curve, the same convergence habit as trail tracing.
Slope — is the boundary longer on hills?
Map perimeter is horizontal (plan) length, matching deeds and fence plans drawn on paper. Fencers on steep ground order a margin for the slope's extra run.
Units for a building site?
Feet for US construction, metres nearly everywhere else — the calculator speaks both so the lumber order and the permit agree.
Perimeter of a circle on the map?
Draw a many-sided polygon to approximate it, or compute 2πr directly with the radius family — the Circle Circumference tools live one click away in the related list.
Coastlines — is the perimeter infinite?
Coastlines grow with measurement fineness (the famous paradox), so a coastline 'perimeter' must always quote its vertex spacing. Field and parcel boundaries, being legally straight segments, are mercifully finite.
Related tools and resources
Its area: the Map Area Calculator; fences: the Fence Length Calculator; open paths: the Trail Distance Estimator.
More free tools
Sources, methodology & editorial trust
- ✓ Browser-first processing where supported
- ✓ External sources are documented
- ✓ No account required for public tools
- ✓ Review data sources
Calculations are documented with their assumptions, limitations and source context rather than presented as unexplained answers.
Reviewed and maintained by Aryan Khan, Founder & Editor of MapBench.
Part of our area & acreage hub
Perimeter Calculator sits in the area & acreage cluster, alongside 26 other tools that answer neighbouring questions with different methods or datasets.
You may also need
When this answer is only part of the job, these clusters cover the next step.
Read the guide behind this tool
How to Measure Fence Length and Count Posts — Measure the run on a map, allow for gates, corners and terrain, and work out how many posts and panels a fence actually needs.