Guide · Calculator
How to calculate floor area from plans for flooring
Floor area for a flooring quote comes from the internal room dimensions printed on the working drawings, split into simple shapes and totalled per finish. Add the shapes below, subtract islands and voids, and the calculator totals each finish in square metres and square feet. The method is explained step by step underneath.
Read the dimension strings, not the drawing
Working drawings carry rows of dimensions, called dimension strings, around and through the plan. The outer strings give overall and external sizes, usually to the outside of the external walls. The inner strings, and the figures written inside each room, give internal room dimensions from wall face to wall face. For flooring you want the internal ones, because the floor stops at the wall.
Builder plans in Australia give dimensions in millimetres, so a room marked 4200 × 3800 is 4.2 m by 3.8 m, or 15.96 m². If a room only has external dimensions, you have to take the wall thicknesses off yourself. Internal walls in many Australian homes are a 90 mm timber or steel stud with plasterboard on both faces, while brick internal walls, common in Perth, are thicker. Check the wall types on the plan or the specification rather than assuming a figure.
Some drafters dimension rooms to the frame rather than the lining, so a built room can measure a few centimetres smaller, well inside a normal waste allowance. The takeoff vs measure-up guide covers when that difference matters.
Why you should not scale a PDF
Most plans state a scale, such as 1:100 at A1. That scale is only true on paper of that size. Print an A1 sheet on A3 and every line is half as long, so the drawing is now really 1:200. A room that measures 42 mm with a ruler reads as 4.2 m to someone who assumes 1:100, but is actually 8.4 m. PDFs exported with fit to page, or plans scanned and emailed, end up at scales nobody can state. That is why many plans carry a note such as "do not scale, use written dimensions".
Take sizes from the printed figures. If a space genuinely has no dimension, measure against a scale bar drawn on the sheet rather than the stated scale, mark the figure as scaled, and confirm it on site.
Break open plan areas into rectangles
Open plan living, kitchen and meals areas are rarely a single rectangle. Split them into rectangles that do not overlap, using the dimension strings that run through the space. An L-shaped room can be split two ways, and both give the same answer, which makes a useful check.
Take an L-shaped living area that is 8.4 m by 7.2 m overall, with a 3.4 m by 3.0 m corner missing:
| Method | Working | Area (m²) |
|---|---|---|
| Split across | 8.4 × 4.2 + 5.0 × 3.0 = 35.28 + 15.00 | 50.28 |
| Split along | 5.0 × 7.2 + 3.4 × 4.2 = 36.00 + 14.28 | 50.28 |
| Box less the corner | 8.4 × 7.2 − 3.4 × 3.0 = 60.48 − 10.20 | 50.28 |
If two splits disagree, one of the rectangles overlaps another or a strip has been left out. Angled walls are handled the same way: a splayed corner is a triangle taken off a rectangle, half of one setback times the other, and a bay window that projects out is a rectangle with a triangle at each splayed side.
Deduct islands, columns and voids
Anything the floor does not run under comes out of the area. In a kitchen that means the island and the bench runs, deducted 10 cm less deep than the plan shows (and 20 cm less in each direction for an island with a kickboard on every side), because a floating floor runs into the kickboard recess. A structural column or a fireplace hearth comes out at its full size. On an upper floor, the stair void is not floor at all, so deduct it if you measured the landing as one rectangle, and measure the stairs themselves separately with the stairs guide.
Fridge and dishwasher spaces are floored, so leave them out of any cabinet deduction. The robes, recesses and kickboards guide works through a full kitchen.
Robes, doorways and small spaces
Built-in robes are floored to the sliding door line, using the robe depth printed on the plan rather than the shaded shelf. Walk-in robes are measured as rooms. Room rectangles also stop at the wall line, so the floor through each doorway is missing from them. Most contractors add a strip across every opening, often 10 cm deep, as an allowance rather than as part of the room area. The guide to quoting from builder plans shows how that allowance is added after the rooms.
A worked example
Example only
The house and its sizes are made up to show the method. They are the figures the calculator starts with.
A single storey home has hybrid in the open plan living, kitchen and meals, the hall, the study and the entry. The bedrooms and robes are carpet, and the wet areas are tiled by others. The living area is the L-shape above, with a splayed corner by the entry set back 1.2 m along each wall. The island is 2.7 m by 1.1 m on the plan and the back bench run is 3.6 m of 600 mm cabinets, excluding the fridge space.
| Shape | Finish | Size (m) | Area (m²) |
|---|---|---|---|
| Living, kitchen and meals (part A) | Hybrid | 8.4 × 4.2 | 35.28 |
| Living (part B) | Hybrid | 5.0 × 3.0 | 15.00 |
| Island bench, less kickboard recess | Hybrid | 2.5 × 0.9 | −2.25 |
| Kitchen bench run, less kickboard recess | Hybrid | 3.6 × 0.5 | −1.80 |
| Splayed corner in living | Hybrid | 1.2 × 1.2 ÷ 2 | −0.72 |
| Hall | Hybrid | 7.8 × 1.1 | 8.58 |
| Study | Hybrid | 3.0 × 3.2 | 9.60 |
| Entry | Hybrid | 2.0 × 1.8 | 3.60 |
| Hybrid | 67.29 | ||
| Bedroom 1 | Carpet | 4.2 × 3.8 | 15.96 |
| Walk-in robe | Carpet | 2.4 × 1.8 | 4.32 |
| Bedroom 2 | Carpet | 3.4 × 3.1 | 10.54 |
| Bedroom 3 | Carpet | 3.2 × 3.0 | 9.60 |
| Robes, bedrooms 2 and 3 (two at 1.8 × 0.6) | Carpet | 3.6 × 0.6 | 2.16 |
| Carpet | 42.58 | ||
| Both finishes | 109.87 |
That is 67.29 m² of hybrid (724.30 sq ft) and 42.58 m² of carpet (458.33 sq ft), 109.87 m² in all (1,182.63 sq ft). These are net floor areas. Doorway strips, waste and rounding to packs or roll lengths come next.
Check your total against the area schedule
Most builder plans carry an area schedule listing living, garage, alfresco and porch areas. It is a good sense check, but your flooring total will not match it, and it should not. The living area in a schedule is usually measured to the outside face of the external walls, so it includes every wall in the house, the wet areas, the laundry and the floor under the joinery. A flooring area is the floor you actually cover.
Example only
Say the example home's schedule lists a living area of 146.80 m². The hybrid and carpet come to 109.87 m², and the tiled wet areas measure 16.90 m² from the same plan, 126.77 m² in total. The remaining 20.03 m² is mostly wall thickness, plus the 4.77 m² of island, bench and splayed corner deducted above.
Look for a gap that makes sense. If your floor areas add up to more than the living area, something is counted twice or the garage has crept in. If the gap is far larger than the walls explain, a room is missing.
Feet and inches
Imperial plans write sizes as feet and inches, such as 12'6" × 10'9". Turn the inches into a fraction of a foot by dividing by 12, so 12'6" is 12.5 ft and 10'9" is 10.75 ft, and multiply: 134.38 sq ft. Switch the calculator to feet and enter decimal feet. One square metre is 10.764 sq ft, so that room is 12.48 m².
From floor area to an order
Floor area is the start of the quote, not the end. Hard floors are rounded up to whole packs after waste, which the hybrid flooring calculator does, and carpet is ordered in lineal metres off the roll, covered in the carpet lineal metres guide. Keep each finish separate, because each is bought, wasted and priced differently.
How Squaro does it
Squaro reads the PDF plan set and the selections, classifies each space by finish, and measures every room from the printed dimension strings, never by scaling the drawing. Each room shows the page and the dimension text it was measured from, and readings it is less sure of are marked for you to check. Your own rules for robes, recesses, doorways, stairs and waste are applied, and you check every line before the quote goes out. Squaro reads metric plans for now, with feet-and-inch plans planned. See flooring takeoff software for what it reads.
Related reading
- How to quote flooring from builder plansThe full method, from the builder's pack to a priced quote, with a worked hybrid example.
- Robes, recesses and kitchen kickboards in a flooring takeoffMeasuring robes to the door line, flooring recesses, and allowing for the kickboard recess.
- Flooring takeoff vs measure-upWhen to quote from plans, when to measure on site, and how to word the quote.
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