Floor plan dimensions

A label on the wall, and a leader off it

The upper 2.00 m sits on the wall. The lower 2.00 m is the offset leader. On 40 mm of paper, 1/4 in = 1 ft is 1:48 and reads 1.92 m, about 4 percent shorter than the 2.00 m of 1:50.

40 mm of paper

How to read a dimension

A manual dimension is a length written on a segment you traced. On the figure, the upper label sits on the wall and reads 2.00 m. You can move a manual label. The free PNG and the free PDF use labels of that kind. They are a table and a marked image, not an architectural sheet. An automatic leader is the lower mark: an offset dimension line, extension lines back to the wall ends, and the same 2.00 m set out in the margin so it does not cover the wall. The live sheet on the calculator draws those leaders before you pay. The PDF and the SVG of that sheet are the paid files. Walls you did not trace get neither mark.

The sample wall behind both marks is the Elm Cottage reference, 400 pixels from (100, 80) to (500, 80), known length 2.00 m. At 10 pixels per millimetre that is 40 mm of paper at 1:50. The nine leaders on the live sheet are this reference plus four edges of the living room and four edges of the kitchen. The living door, 0.80 m, is not a leader. It is subtracted later, in the takeoff, from a 7.00 m perimeter to leave 6.20 m of skirting. If you never trace the kitchen, the kitchen edges do not appear. The tool does not read the sizes printed on the plan. It does not use OCR, and it does not recognise a room by its shape.

The table under the figure is 40 mm of paper at each scale the converter offers. 40 mm times the ratio, divided by 1,000, is the real length in metres. 1:20 is 0.80 m. 1:50 is 2.00 m. 1:100 is 4.00 m. 1:200 is 8.00 m. 1:500 is 20.00 m. Architectural scales are ratios too. 3 in = 1 ft is 1:4, and 40 mm is 0.16 m. 1 1/2 in = 1 ft is 1:8, 0.32 m. 1 in = 1 ft is 1:12, 0.48 m. 3/4 in = 1 ft is 1:16, 0.64 m. 1/2 in = 1 ft is 1:24, 0.96 m. 3/8 in = 1 ft is 1:32, 1.28 m. 1/4 in = 1 ft is 1:48, 1.92 m. 3/16 in = 1 ft is 1:64, 2.56 m. 1/8 in = 1 ft is 1:96, 3.84 m. 3/32 in = 1 ft is 1:128, 5.12 m. 1/16 in = 1 ft is 1:192, 7.68 m. Rounding is half away from zero to two decimal places.

1/4 in = 1 ft is not 1:50. A quarter of an inch stands for 12 inches, and 12 / 0.25 is 48, so the ratio is 1:48. On 40 mm of paper that is 1.92 m, against 2.00 m at 1:50. The difference is 0.08 m, which is 4 percent of 2.00 m. Areas move by about twice that, near 8 percent, because area uses the square of the scale. On Elm Cottage the 1:48 preset reads 1.92 m on the reference, 2.76 m² in the living room, 1.66 m² in the kitchen, and 4.42 m² overall. The 1:50 figures are 2.00 m, 3.00 m², 1.80 m², and 4.80 m². Mixing the two scales on one takeoff is a larger error than the 10 percent waste line.

You can check the live leaders on the calculator before you pay. The margin column is there so the figures do not collide with each other or with the walls. The paid PDF and SVG use the segments already traced, with extension lines and the same lengths. They do not add a price, a product code, or a watermark. The takeoff pack is a different paid file: floor, skirting after doors, and paint, each with a formula, plus a signature page. The preview of that pack is open under the sheet on the calculator and on the takeoff page. Paying downloads the file. The preview does not upload the drawing.

A length on a scanned sheet is only as good as the scan. If 40 mm of paper is not 400 pixels because the page was cropped or photographed, the table still tells you what the ratio means, and the known wall on the calculator tells you what this particular file means. Prefer the known wall when you have one. Use the table when the title block names a ratio and you have not yet set a wall. Neither replaces measuring on site. The result is not a statutory valuation and not a quantity survey. Return to the floor plan scale calculator to put a ratio or a known wall on the drawing you actually have.

Where these figures get used

Someone staring at a title block that says 1:100 can read 4.00 m for 40 mm of paper in the table, then open the calculator and press 1:100. The Elm Cottage reference, 400 pixels at 10 pixels per millimetre, should read 4.00 m. If it reads something else, the file is not 10 pixels per millimetre and the known wall is the control to trust.

Someone with an imperial title block of 1/4 in = 1 ft should not press 1:50. The table row for 1/4 in = 1 ft is 1.92 m on 40 mm, and the calculator preset is 1:48. The 0.08 m gap on a 2.00 m wall is the 4 percent the figure is here to make obvious. The manual label and the offset leader in the drawing are the same length only when they measure the same segment.

A draftsperson comparing a marked-up PNG with a paid SVG can use the upper label as the free mark and the lower leader as the paid mark. Both say 2.00 m on this wall. The SVG is worth paying for when the sheet has many segments and the labels need extension lines. It is not worth paying for if the scale is still unset: the leaders would be pixel lengths, and the fields would say Not to scale.

Put a known wall or a ratio on the drawing with the floor plan scale calculator. The sheet there opens on Elm Cottage at 2.00 m, with a living room of 3.00 m² and a total of 4.80 m².

Common questions