Whether you're measuring a room for flooring, calculating garden space for turf, or working on a school project, knowing how to calculate area is an essential skill. This guide covers all common shapes with clear formulas and worked examples.
Quick Reference: All Area Formulas
Square
All sides equal length
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Rectangle
Four right angles
Triangle
Three-sided polygon
Circle
Round shape
Parallelogram
Opposite sides parallel
Trapezium
One pair of parallel sides
Rectangle and Square
The most common area calculation—used for rooms, gardens, walls, and more:
Area = Length × Width
Square Formula:
Area = Side × Side = Side²
Example: Room Floor Area
Room dimensions: 5.2m × 4.1m
Calculation: 5.2 × 4.1 = 21.32 m²
Example: Square Patio
Side length: 3.5m
Calculation: 3.5 × 3.5 = 12.25 m²
Triangle
For triangles, you need the base and the perpendicular height:
Area = ½ × Base × Height
Area = (Base × Height) ÷ 2
Example: Triangular Garden Bed
Base: 6m
Height: 4m
Calculation: ½ × 6 × 4 = 12 m²
Alternative Triangle Formula (Heron's Formula)
When you know all three sides but not the height:
s = (a + b + c) ÷ 2
Area = √(s × (s-a) × (s-b) × (s-c))
Where a, b, c are the three side lengths and s is the semi-perimeter
Circle
Circles use π (pi ≈ 3.14159) and the radius (distance from centre to edge):
Area = π × r²
Circle Formula (using diameter):
Area = π × (d ÷ 2)² = π × d² ÷ 4
Example: Circular Patio
Diameter: 4m (Radius = 2m)
Calculation: 3.14159 × 2² = 3.14159 × 4 = 12.57 m²
Semicircle
Area = (π × r²) ÷ 2
L-Shaped and Irregular Rooms
For irregular shapes, divide them into rectangles and triangles:
Example: L-Shaped Room
Main area: 5m × 4m = 20 m²
Extension: 2m × 3m = 6 m²
Total: 20 + 6 = 26 m²
Parallelogram
Area = Base × Perpendicular Height
Note: Use perpendicular height, not the slanted side
Trapezium (Trapezoid)
A four-sided shape with one pair of parallel sides:
Area = ½ × (a + b) × h
Where a and b are the parallel sides, h is the perpendicular height
Example: Trapezoid Garden
Parallel sides: 8m and 5m
Height: 4m
Calculation: ½ × (8 + 5) × 4 = ½ × 13 × 4 = 26 m²
Ellipse (Oval)
Area = π × a × b
Where a and b are the semi-major and semi-minor axes (half the long and short diameters)
Converting Area Units
| From | To | Multiply By |
|---|---|---|
| m² | cm² | 10,000 |
| m² | ft² | 10.764 |
| ft² | m² | 0.0929 |
| m² | yards² | 1.196 |
| acres | m² | 4,047 |
| hectares | m² | 10,000 |
Common Area Sizes
| Item | Typical Area |
|---|---|
| A4 paper | 0.062 m² |
| Parking space | 12 m² |
| Single bedroom | 9-11 m² |
| Double bedroom | 12-15 m² |
| Living room | 15-25 m² |
| Football pitch | 7,140 m² (average) |
| Tennis court | 261 m² |
| Olympic swimming pool | 1,250 m² |
Practical Applications
Flooring
Calculate floor area, then add 10% for cutting waste:
- Measure room length × width
- Calculate total m²
- Add 10% for waste
- Divide by coverage per pack
Paint Coverage
For walls, calculate (perimeter × height) - doors/windows
Turf/Seeds
Measure garden area, turf typically sold per m²
Tips for Accurate Measurements
- Measure twice: Double-check all measurements
- Use a long tape: 5m or longer for rooms
- Note down immediately: Don't rely on memory
- Sketch the shape: Draw a rough diagram with dimensions
- Break down complex shapes: Split into rectangles and triangles
- Account for alcoves: Add or subtract as needed
Understanding Area in UK Property and Planning
Area calculations play a critical role in the UK property market and planning system. Estate agents are required to follow the Royal Institution of Chartered Surveyors (RICS) guidelines when measuring property floor areas, using the Gross Internal Area (GIA) or Net Internal Area (NIA) depending on the type of property. GIA measures the total enclosed floor space within the external walls, while NIA excludes internal structural walls, stairwells, and service areas. Understanding these distinctions helps buyers compare properties accurately.
The Nationally Described Space Standard (NDSS), introduced in 2015 for new-build homes in England, sets minimum floor area requirements based on the number of bedrooms, occupants, and storeys. A one-bedroom, one-person dwelling must have at least 39 square metres of floor space, while a three-bedroom, five-person home spread across two storeys requires a minimum of 93 square metres. Local planning authorities can adopt these standards as part of their local plans, making area calculation essential for developers and architects working on residential projects.
Garden and outdoor area calculations are equally important for UK homeowners. Planning permission for outbuildings, extensions, and conservatories often depends on the total area of land covered by structures relative to the overall garden size. Under permitted development rights, outbuildings must not cover more than 50 percent of the land surrounding the original house. Calculating the combined area of sheds, garages, greenhouses, and proposed new structures against the total garden area determines whether planning permission is needed.
Total garden area - (sum of all building footprints) = remaining open space
If remaining space is less than 50% of garden, planning permission is likely needed
Area Calculations for Home Improvement Projects
Accurate area calculations directly affect the cost and success of home improvement projects. When ordering flooring, whether laminate, vinyl, carpet, or tiles, you need to calculate the room area and add a waste allowance. The standard waste allowance is 10 percent for rectangular rooms with straightforward layouts, rising to 15 percent for rooms with alcoves, bay windows, or diagonal laying patterns. For tiles, waste can reach 20 percent in small bathrooms where many cuts are needed around sanitary ware.
Wall area calculations are essential when buying paint, wallpaper, or plaster. To calculate the total wall area of a room, multiply the room perimeter by the ceiling height, then subtract the area of windows and doors. A standard internal door opening is approximately 1.98 square metres, while a typical window is around 1.2 square metres. One litre of standard emulsion paint covers approximately 12 to 14 square metres per coat, so a room with 45 square metres of wall area requiring two coats needs roughly 7 litres of paint.
For turfing or seeding a lawn, measure the garden area carefully and consider the shape. Many UK gardens are not simple rectangles but include curved borders, flower beds, and pathways that must be subtracted from the total area. Turf is typically sold in rolls of approximately 1 square metre each, while grass seed is sold by weight with coverage rates of roughly 25 to 35 grams per square metre for a new lawn.
Frequently Asked Questions
How do I calculate the area of a bay window recess?
A bay window recess is typically a trapezium shape. Measure the width at the back wall (the wider parallel side), the depth from the back wall to the front of the bay, and the width across the front of the bay (the narrower parallel side). Apply the trapezium formula: Area = half multiplied by the sum of the two parallel sides, multiplied by the depth. For a Victorian bay with a back width of 2.5 metres, front width of 1.8 metres, and depth of 0.9 metres, the area is 0.5 x (2.5 + 1.8) x 0.9 = 1.94 square metres.
What is the difference between square metres and metres squared?
Although these terms sound similar, they can be confused in different contexts. Square metres (m2) is a unit of area measurement, representing the space covered by a square with sides of one metre. A room that is 4 metres by 3 metres has an area of 12 square metres. The term "metres squared" technically refers to the mathematical operation of squaring a length measurement, though in everyday usage, most people use the two phrases interchangeably. For clarity, always specify whether you are referring to a linear measurement or an area when communicating dimensions.
How do I calculate the area of a room with an alcove?
Treat the room as a rectangle first, then add the area of the alcove separately. Measure the main room dimensions and calculate its area. Then measure the alcove width and depth and calculate that area. Add the two together for the total room area. For example, a room that is 4 metres by 3 metres with a chimney breast alcove measuring 1 metre by 0.5 metres has a total area of 12 + 0.5 = 12.5 square metres. If the alcove reduces the room size rather than extending it, subtract instead of adding.
Frequently Asked Questions
How do I calculate the area of an irregularly shaped UK garden or plot?
What units of area measurement are commonly used in the UK?
UK Property Measurements and HM Land Registry Standards
Accurate area calculation is particularly important in the UK property market, where floor area directly influences valuations, stamp duty calculations, and Energy Performance Certificate (EPC) ratings. HM Land Registry, the government body responsible for registering property ownership in England and Wales, records property boundaries using Ordnance Survey mapping data, and title plans show the general extent of registered land. The Royal Institution of Chartered Surveyors (RICS) sets the professional standards for property measurement in the United Kingdom through its Code of Measuring Practice, which defines Gross Internal Area (GIA), Gross External Area (GEA), and Net Internal Area (NIA) as the three principal measurement conventions used across the UK property industry.
For residential property in the United Kingdom, estate agents typically quote floor area using Gross Internal Area, which measures the area enclosed by the internal face of external walls, including internal walls, staircases, and built-in storage but excluding external balconies and terraces. Commercial property transactions more commonly use Net Internal Area, which deducts common areas such as lobbies, staircases, and WCs from the gross figure. Since 2024, the UK government has strengthened requirements around property listing accuracy, and the National Trading Standards Estate and Letting Agency Team has increased enforcement action against agents who publish misleading floor area figures. For consumers buying or selling property, verifying area measurements against the original floor plan or commissioning an independent RICS survey provides essential protection against overstatement, which research by the Property Ombudsman has identified as one of the most common sources of complaint in UK residential transactions.
Emma Thompson
Senior Content Editor
Emma is a senior content editor with a background in financial journalism. She specialises in making UK regulations and calculator tools understandable for consumers, working closely with qualified professionals to ensure accuracy.