Irregular Lawn Shape Calculator UK — Triangle, L-Shape, Circle & Free-Form
UK Irregular Lawn Tool

Irregular Lawn
Shape Calculator UK

Calculate the area of any awkwardly shaped UK garden lawn — triangle, L-shape, circular section, trapezoid, and free-form grid estimation. Add multiple shapes and get a combined total in m².

Triangle L-Shape Circular Section Free-Form Grid
Open Calculator Measuring Methods
Calculator

Irregular Lawn Shape Calculator

Select your lawn shape, enter measurements, and click Calculate. Add multiple sections to build a combined total.

Multi-Shape Irregular Lawn Calculator

6 shape types · Running total · All results in m²

Select Your Lawn Shape

Length Width

Simple rectangle or square lawn section.

A = L × W
h base

Any triangle — right-angled, isosceles, or scalene corner lawn.

A = ½ × B × H

How to measure: The base is any one side of the triangle. The height is the perpendicular (90°) distance from that base to the opposite corner — not along the sloped side.

A×B C×D

Split L into two rectangles. Measure each part separately.

A = (A×B)+(C×D)

Tip: Imagine a horizontal or vertical line that divides your L-shape into two rectangles. Measure the length and width of each rectangle separately, then the calculator adds them together.

radius

Full circle, half circle, or custom arc section.

A = π × r²
Full width across the circle
H Side A Side B

A tapered or wedge-shaped lawn — wider at one end.

A = ½(A+B)×H

How to measure: Measure both parallel sides (A and B — the two ends that run parallel to each other), then measure the perpendicular distance between them (Height H).

Free-Form Grid Method: Each coloured square represents a real-world cell. Set the cell size (in metres), then click squares to paint the shape of your lawn. The calculator counts selected cells and multiplies by the cell area. This is the UK professional grid-counting method for oddly shaped lawns with curved edges.

m × m per cell
0 cells selected · 0.00 m²

 Running Total — All Lawn Sections

#LabelShapeCalculationArea
Total Lawn Area
0
m²
Equivalents
0 ft²
0 yd²
Seed estimate @ 35 g/m²
0 kg
standard sowing rate
Methods

How to Measure an Irregular UK Lawn

The best method depends on your lawn shape and how accurate you need to be. Here are the four main professional approaches.

1

Divide & Conquer

Sketch your lawn and draw straight lines to divide it into simple rectangles, triangles, and circles. Calculate each section separately and add the areas. Works for most UK domestic lawns — accurate to within 2–3%.

Most Accurate
2

Grid Counting

Lay a measured grid over a scale drawing of your lawn (or use the grid tool above). Count full squares plus roughly half of partial squares at the edges. Multiply the count by the real size of each grid square. Used by professional landscapers for irregular curved lawns.

3

Offset / Running Tape

Run a tape measure along the longest straight edge (the baseline). At regular intervals (every 0.5–1m), measure the perpendicular width of the lawn from the baseline to the curved edge. Average all widths, then multiply by the total baseline length. Excellent for kidney-shaped or curved lawns.

4

Triangle Breakdown

For very irregular polygon shapes, divide the area into multiple triangles radiating from a central point. Measure the base and height of each triangle, calculate each area using ½ × B × H, and sum all results. This is how surveyors handle complex irregular plots.

💡 UK Pro Tip: For a family garden with curved borders, the offset/running tape method is fastest. Use a 20m tape along the straightest edge, take perpendicular measurements every 1 metre, average them, and multiply by the total length. For a 10m lawn with average width 6m, that gives 60 m². Always add 10% to any material order as a buffer.
Formula Reference

UK Lawn Shape Formula Guide

Quick reference for every shape formula used in this calculator — all inputs in metres, all results in m².

Swipe table left on mobile
Shape Inputs Formula Example Result
Rectangle / Square Length (L), Width (W) A = L × W 12m × 8m 96 m²
Right-Angle Triangle Base (B), Height (H) A = ½ × B × H 9m × 6m 27 m²
L-Shape A, B (rect 1) + C, D (rect 2) A = (A×B) + (C×D) (10×4)+(6×5) 70 m²
Full Circle Diameter (d) A = π × (d÷2)² ⌀ 6m 28.27 m²
Semicircle Diameter (d) A = ½ × π × (d÷2)² ⌀ 6m 14.14 m²
Quarter Circle Diameter (d) A = ¼ × π × (d÷2)² ⌀ 6m 7.07 m²
Trapezoid Side A, Side B (parallel), Height H A = ½ × (A+B) × H 5m, 9m, H=7m 49 m²
Free-Form (Grid) Cells selected, Cell size (m) A = Cells × (size × size) 48 cells × 0.5m² 12 m²
Step-by-Step

How to Use This Calculator

Three simple steps to calculate your total irregular lawn area in m².

1

Sketch & divide your lawn

Grab a piece of paper and sketch the outline of your lawn. Draw straight lines to divide it into the simplest possible shapes — rectangles, triangles, circles, and L-shapes. Label each section A, B, C, etc. Most irregular UK lawns can be divided into 2–4 sections.

2

Measure each section

Measure the required dimensions of each section with a tape measure — length and width for rectangles, base and perpendicular height for triangles, diameter for circles. Write each measurement on your sketch. Always measure to the nearest 10cm (0.1m) for accuracy.

3

Calculate & add to total

Select the matching shape tab, enter your measurements, click Calculate, then click Add to Running Total. Repeat for each section. The calculator accumulates all sections and shows your combined total area in m², plus a seed estimate at standard sowing rate.

FAQ

Frequently Asked Questions

Common questions about measuring and calculating irregular UK lawn shapes.

The easiest approach is to divide the lawn into simpler geometric sections — rectangles, triangles, and circular arcs. Sketch the shape on paper, draw lines to divide it into manageable pieces, and measure each section separately with a tape measure. Add all the section areas together for the total. For curved edges, the offset method (measuring perpendicular widths at regular intervals along a baseline) gives accurate results without complicated geometry.
For any triangle, the formula is Area = ½ × Base × Height. The base is one side of the triangle. The height is the perpendicular distance from that base to the opposite corner — measured at exactly 90° to the base, not along the sloped side. For a right-angled corner (very common in UK gardens), the two shorter sides are the base and height. Simply measure both sides of the right angle and multiply: ½ × side1 × side2.
Draw a horizontal or vertical line across the notch of the L to divide it into two rectangles. You can cut the L-shape at any convenient point — either across the top or down the side. Measure the length and width of each rectangle separately, calculate each area (L×W), then add them together. The calculator's L-Shape tab does this automatically. Some people prefer to calculate the full bounding rectangle then subtract the missing corner — both methods give identical results.
Use the offset measurement method. Lay a tape measure along the longest straight edge of the lawn (the baseline). Every half metre or every metre, measure the perpendicular distance from the tape to the curved edge of the lawn. Record all measurements, add them together, then divide by the number of measurements to get the average width. Multiply average width by the total baseline length for the approximate area. This is accurate to within 3–5% for most curved UK garden lawns.
For a full circle, measure the diameter (the widest distance across) and use the formula: Area = π × (diameter ÷ 2)². For a semicircle (half circle), divide the full circle result by 2. For a quarter circle, divide by 4. The calculator's Circle/Arc tab handles all of these automatically — you only need to enter the diameter and select the arc type. For a custom circular section (such as a three-quarter circle), select "Custom Arc %" and enter the percentage of the full circle your lawn represents.
Grid counting involves overlaying a measured grid over a scaled drawing of your lawn and counting how many grid squares fall within the lawn boundary. Full squares count as 1, partial squares at the edges are counted as 0.5. Multiply the total count by the real-world area of each grid cell. This method is accurate to within 2–5% for most irregular shapes. The free-form grid tool above uses this exact method — click to select cells that represent your lawn shape, set the cell size in metres, and the calculator does the rest.
Once you have your total lawn area in m², multiply by the seed rate shown on your seed bag. Standard UK perennial ryegrass or fescue lawn seed is applied at 35g/m² for a new lawn, or 20–25g/m² for overseeding. For a fine bent grass or fescue/bent mix, rates vary between 10–50g/m² depending on the mixture. The running total panel in this calculator automatically shows a seed estimate at 35g/m² as a guide. Use our Bent Grass Seed Calculator for more precise rates on fine lawn mixes.
A trapezoid (or trapezium in British English) is a four-sided shape where two sides are parallel but of different lengths. Many UK gardens have this shape — wider at one end, narrower at the other, due to housing plot boundaries or tapering pathways. Measure both parallel sides (A and B — the two ends), then the perpendicular height between them (H) — the straight distance from one parallel side to the other, measured at 90°. The formula is: Area = ½ × (A + B) × H.
The perpendicular height of a triangle is the straight-line distance from one side (the base) to the opposite corner, measured at exactly 90° to the base. For a right-angled triangle (a corner-shaped lawn), the two legs of the right angle are already perpendicular to each other — just measure both sides of the right angle. For a non-right-angled triangle in your garden, stand at the opposite corner from your chosen base, walk towards the base keeping the right angle between you and the base end points, and measure the distance at that 90° point.
Yes — this is exactly what the calculator is designed for. Calculate each section of your lawn using the appropriate shape tab, then click "Add to Running Total" after each calculation. The running total panel at the bottom accumulates all sections, shows a breakdown table of every shape added, and displays the combined total in m², ft², and yd², plus a grass seed estimate. You can remove individual entries or clear the entire total and start again at any time.
For practical purposes — ordering grass seed, turf, or fertiliser — measuring to the nearest 10cm (0.1m) is more than sufficient. A 5% inaccuracy on a 100 m² lawn represents only 5 m² — equivalent to about half a bag of grass seed. Always add 10% to any material order regardless of measurement accuracy to account for wastage, irregular coverage, and edge losses. The cost of ordering 10% too much seed is always less than the cost of running out mid-job and making an emergency purchase.
UK garden sizes vary enormously by property type and region, but typical back garden lawn areas (excluding beds, paths, and patios) are: terraced house — 15–40 m², semi-detached house — 40–100 m², detached house — 80–200 m², and larger detached/rural properties — 200 m²+. Northern England properties typically have slightly larger gardens than equivalent properties in London and the South East. Many UK gardens are irregular in shape due to historic plot boundaries, which is why tools like this calculator are needed.
To convert square metres to square feet, multiply by 10.764. For example, 80 m² × 10.764 = 861 ft². To convert back from square feet to square metres, divide by 10.764. The running total panel in this calculator automatically shows your combined area in both m² and ft². All UK lawn product packaging and supplier coverage rates now use m² as the standard unit, so working in metric throughout avoids conversion errors when ordering materials.

Now calculate your seed requirements

You have your lawn area in m² — use our Bent Grass Seed Calculator to find out exactly how much fine lawn seed you need for a luxury UK finish.

Bent Grass Seed Calculator