Basics
Scale 1:100 on a floor plan
A scale of 1:100 means one centimetre on paper equals one metre in reality. A room 4.20 metres wide is 4.2 centimetres wide on the drawing. There is nothing more to the ratio — which is exactly why it is so often used incorrectly.
Because the ratio only holds for one particular sheet size. As soon as somebody prints the page reduced, photocopies it or zooms on screen, the printed ratio is wrong even though the drawing itself is unchanged and correct.
Which scale for what
1:100 is the standard for residential plans. A typical dwelling fits an A4 sheet and room names stay readable. For a larger house you move to A3 at the same scale rather than switching to 1:200.
1:50 is for detail drawings, bathrooms, kitchens and fit-out work, where centimetres matter. 1:200 suits large buildings, commercial space and floors with many units, where overview beats detail.
- 1:50 — detail, bathroom, kitchen, fit-out
- 1:100 — flats, houses, the listing standard
- 1:200 — large buildings, commercial, whole floors
- Choose the scale to fit the sheet, not the reverse
Why a scale bar is more reliable
A scale bar is a drawn bar divided in metres. It scales with the drawing when the page is enlarged or reduced, so it stays correct even on a copy of a copy and on a screen at any zoom level.
The printed "1:100" is by contrast a claim about the paper. So put both on the plan: the ratio to set the expectation, and the bar as the reference anyone can actually check against.
Measuring and verifying
To test whether a plan is to scale, measure two distances on site that lie far apart and compare with the drawing. If both deviate proportionally, the scale is wrong; if only one does, there is a drafting error at that point.
Anyone who has to measure reliably should not measure a PDF at all but request a DXF. There the geometry sits in millimetres and is independent of any sheet size.
Frequently asked questions
What exactly does 1:100 mean?
One centimetre on the drawing equals one metre in reality. A room four metres wide is four centimetres wide on paper.
Which scale is usual for a property listing?
1:100. A typical dwelling fits A4 and stays readable. For larger houses you change the sheet size rather than the scale.
Why is the scale wrong in my print-out?
Because the print dialogue rescaled it, or the sheet size differs. The scale bar stays correct in both cases, because it scales with the drawing.