Farm Field Area Calculator: Measure Paddocks and Fields From Satellite
Use this interactive farm field area calculator to measure paddocks, fields, and land parcels directly from satellite imagery. Draw as many fields as you need, name each one, and get instant area readings in hectares, acres, square kilometres, square miles, or square metres. Download all your boundaries as GeoJSON, GPX, or KML for use in farm management software, GPS units, or Google Earth.
How to Use This Farm Field Area Calculator
Step 1: Navigate to Your Farm
Use the address search bar on the map to find your property, or pan and zoom manually. Switch between ESRI Satellite, Google Satellite, and OpenStreetMap using the layer control in the top-right corner. Zoom in to zoom level 13 or higher before drawing — at this level, individual fields and hedgerows are clearly visible.
Step 2: Draw Your Fields
Click Draw Field (Freeform) to trace any irregular field shape, clicking once per point and double-clicking to finish. Use Draw Field (Rectangle) for square or rectangular paddocks. Each field is assigned a different colour automatically. Fields snap to nearby boundaries — an orange ring indicator appears when your cursor is close enough to snap to an existing edge or vertex, helping you create clean, gap-free farm maps.
Step 3: Name Your Fields
Each new field is named “Field 1”, “Field 2”, and so on. Click any name in the results table to rename it — for example “North Paddock”, “Wheat Block 3”, or “River Flat”. Names carry through to all downloaded files.
Step 4: Edit Field Shapes
Click Edit Fields to enter edit mode. All drawn polygons display draggable vertex handles. Drag any vertex to reshape a boundary, or drag the midpoint handles to add new vertices. Click Save Edits to commit changes — areas recalculate instantly. Click Cancel to revert all edits.
Step 5: Choose Units and Download
Use the unit toggle above the table to switch between ha / ac, km² / mi², or m² / ha. The “All units” summary bar always shows the total farm area expressed in all five units simultaneously. When you are ready, download the complete set of field boundaries using the GeoJSON, GPX, or KML buttons.
Units of Measurement
The calculator supports five area units, all derived from the geodesic area of your drawn shapes:
- Hectares (ha) — the standard unit for farm land in Australia, New Zealand, Europe, and most of the world. 1 ha = 10,000 m².
- Acres (ac) — the primary land measurement unit in the United States and commonly used alongside hectares in the UK and Australia. 1 acre = 4,046.86 m².
- Square kilometres (km²) — useful for large properties, stations, and ranches. 1 km² = 100 ha.
- Square miles (mi²) — used for large land parcels in the US. 1 mi² = 640 acres = 258.999 ha.
- Square metres (m²) — useful for small plots, orchards, market gardens, and precise comparison work.
Download Formats Explained
GeoJSON
The recommended format for GIS workflows. Each field is stored as a GeoJSON Feature with its name and area values in all five units as properties. Compatible with QGIS, ArcGIS, Mapbox, Google Earth Engine, and any modern web mapping library. Open the file in any text editor to inspect or edit the raw coordinates.
KML
Keyhole Markup Language — the native format for Google Earth and Google My Maps. Each field appears as a labelled polygon with its area in the description. Compatible with most GPS receivers and farm management platforms that accept spatial imports.
GPX
GPS Exchange Format — widely supported by Garmin, Trimble, and other GPS devices used in agriculture. Field boundaries are stored as tracks (one track per field), which can be loaded onto handheld GPS units and followed on foot or in a vehicle. Useful for physically locating boundary corners on the ground or for importing into farm recording systems.
Boundary Snapping
When drawing freeform polygon fields, the tool automatically snaps new vertices to nearby boundaries of existing fields. This uses two levels of snapping:
- Vertex snapping — if your cursor is within 15 pixels of an existing corner point, the new vertex will lock exactly to that point.
- Edge snapping — if your cursor is near the middle of an existing field edge, the new vertex snaps to the closest point on that edge.
An orange circle indicator appears on the map when snapping is active. This makes it straightforward to draw adjacent paddocks that share clean, gap-free boundaries — important for accurate total farm area calculations and clean exports.
Accuracy and Limitations
Area calculations use the Turf.js geospatial library, which computes geodesic area from WGS84 coordinates — meaning the curvature of the Earth is accounted for. This gives accurate results anywhere in the world, including at high latitudes where map projections introduce the most distortion.
Practical accuracy depends on:
- Satellite image resolution — high-resolution imagery (ESRI or Google satellite) in populated agricultural regions is typically accurate to 1–3 metres. Rural and remote areas may have lower-resolution imagery.
- Drawing precision — trace field boundaries at the highest practical zoom level for the most accurate outlines. Rough outlines will still give useful ballpark figures.
- Image age — satellite imagery may be months or years old and may not reflect recent changes to field layouts.
For legal, surveying, or regulatory purposes always verify with an accredited land surveyor.
Frequently Asked Questions
How do I measure an irregularly shaped paddock?
Use Draw Field (Freeform) and click carefully around the paddock boundary, following fence lines or visible field edges in the satellite imagery. Add as many points as you need to capture curves and irregular corners. Double-click to close the shape.
Can I draw multiple fields and get a total area?
Yes. Draw as many fields as you need — each appears in the table with its individual area. The total row at the bottom of the table shows the combined area across all drawn fields, and the “All units” bar shows this total in every unit simultaneously.
Can I edit a field after drawing it?
Yes. Click Edit Fields to enter edit mode. All polygon vertices become draggable. Reshape any field by dragging its vertices, then click Save Edits. Areas update automatically.
What file format should I use for my GPS unit?
Most handheld GPS devices used in agriculture (Garmin, Trimble, TopCon) accept GPX files. Download the GPX and transfer it to your device via USB or the manufacturer’s software. Field boundaries will appear as tracks on the GPS screen.
What file format works with QGIS or ArcGIS?
GeoJSON is the most portable and widely supported. Both QGIS and ArcGIS (Pro and Online) can open GeoJSON directly. The downloaded file includes area values in all five units as feature attributes, which will appear in the attribute table.
How accurate is the area calculation?
For a carefully traced 100-hectare field, expect accuracy within 1–2% of a GPS survey, depending on image resolution and drawing precision. Geodesic calculation means there is no systematic error due to map projection.
Does this work for properties in Australia, New Zealand, and the US?
Yes — the tool works globally. Australian and New Zealand users typically work in hectares; US users in acres. Both are shown by default in the ha / ac unit mode, and all five units are always visible in the summary bar.
About This Tool
This farm field area calculator is built on Leaflet with drawing capabilities from Leaflet.draw and geodesic area calculation from Turf.js. All processing happens in your browser — no data is sent to any server.
