Irregular area calculator
Draw your outline, adjust its corners, and see boundary lengths, area and perimeter. Exact coordinate entry is available under Advanced.
PDF: choose Save as PDF in the print dialog. Sharing sends the calculator link only, without your measurements.
Draw or enter your outline
Use actual measurements in one unit. Join corners in order around the boundary; the final edge closes automatically.
Click a line to select it. Drag from an edge to add a corner, or use Add corner on selected line. The grid starts at 0–20 by 0–13 in your chosen unit and scales with fitted outlines. For larger or more precise shapes, open Advanced: Enter exact coordinates.
A little help with measuring
Use matching units for every dimension. A radius is half the diameter; an ellipse uses two radii. A perpendicular height is measured at 90° to the base.
For an irregular plot, enter each corner in order around its boundary. Concave shapes work too. For holes or curved boundaries, calculate separate pieces and add or subtract their areas using the everyday calculator.
Side lengths alone don’t determine the area of an irregular polygon. Custom mode therefore uses corner coordinates. This calculator measures flat, two-dimensional shapes; it does not calculate 3D surface areas.
- Perimeter / boundary
More units and calculation details
- Square metres
- Square feet
- Acres
- Hectares
The main perimeter is displayed to a maximum of two decimal places; other results use 10 significant figures. Calculations retain full internal precision. Changing units converts your existing dimensions and coordinates, preserving the physical size.
Advanced: Enter exact coordinates
How to measure an irregular shape
- Draw your outline, or try an example below.
- Drag corners to adjust the shape. Select a line to enter its exact length.
- Read the updated area, perimeter and boundary measurements. Change units to convert the same physical outline.
Changing a line moves one corner, so an adjoining line and the area may change too. Lengths are not locked. Side lengths alone do not uniquely determine an irregular shape’s area.
Worked examples for your room, garden or patio
An L-shaped room
Area: 26 m² · Perimeter: 22 m
A 6 m × 5 m room with a 2 m × 2 m corner removed has an area of 30 − 4 = 26 m². Its perimeter is 22 m, and its area is 279.9 ft² to one decimal place.
Exact coordinates (metres)
0, 0 6, 0 6, 3 4, 3 4, 5 0, 5
A garden with a stepped boundary
Area: 70 m² · Perimeter: 38 m
A 10 m × 9 m rectangle with a 5 m × 4 m corner removed has an area of 90 − 20 = 70 m². Its perimeter is 38 m.
Exact coordinates (metres)
0, 0 10, 0 10, 5 5, 5 5, 9 0, 9
A patio beside a flower bed
Area: 34 m² · Perimeter: 26 m
An 8 m × 5 m patio footprint with a 3 m × 2 m corner left for planting has an area of 40 − 6 = 34 m². Its perimeter is 26 m.
Exact coordinates (metres)
0, 0 8, 0 8, 3 5, 3 5, 5 0, 5
How the calculation works, coordinates and precision
Entering exact coordinates
Choose one corner as your origin, (0, 0). Measure each corner’s horizontal x and vertical y distance from that same origin. Enter corners in boundary order, one x, y pair per line, in Advanced: Enter exact coordinates. The final edge closes automatically.
What the results mean
The calculator uses the shoelace formula for area and adds the lengths of all boundary segments for perimeter. Coordinates may be negative and the outline may be concave, but edges must not cross or touch each other. Enter 3–200 distinct corners and do not repeat the first corner.
This tool measures a flat, straight-edged outline. For holes, calculate the outer and inner areas separately and subtract them. Approximate curved edges with measured straight segments, or use the appropriate shape in Area & Shapes.
Drawing grid and precision
The interactive grid starts at x = 0–20 and y = 0–13 in the selected unit. Outlines outside that grid are fitted to view with a scaled measurement grid and can be edited through exact lengths or coordinates. After a unit conversion, a larger numerical outline may therefore need coordinate editing. Turning snapping off permits drawing steps of 0.01 unit; typed coordinates support finer measurements.
The main perimeter is displayed to a maximum of two decimal places; other results use 10 significant figures. Calculations retain full internal precision. Converted measurements retain extra precision internally, but ordinary floating-point rounding can occur. For paving, flooring or turf, the calculated area excludes cutting waste and ordering allowances. Check your measurements before ordering materials.
Use all Numbers tools for arithmetic and conversions, or calculate a regular eight-sided shape with the octagon area calculator.