Published 2026-08-29 · 2 min read
Dimensions and scale in a floor plan: reading and drawing them
A plan without dimensions is a sketch. Builders do not measure paper with a ruler — they read numbers. Here are the rules every usable plan follows, whatever program drew it.
What scale means
1:50 means one centimetre on paper is fifty centimetres in reality. A 5 m wall appears as 10 cm. At 1:100 that same wall is 5 cm — more house fits on the sheet, but fewer details are visible.
The choice is not aesthetic: 1:50 for construction drawings, where thicknesses and openings must read; 1:100 for presentation and permits; 1:20 for details such as a stair junction.
Three dimension lines, in order
Dimensions are not scattered wherever there is room. They sit outside the plan on three parallel lines, running outward from the building outline:
- First line, closest: openings — the width of each window and door, with the solid pieces between them.
- Second: structural axes, the distances between centres of load-bearing walls or columns.
- Third, furthest out: overall dimensions on each side.
- Inside, dimension only what cannot be deduced: each room's size and internal wall thicknesses.
Opening, axis and clear dimensions
An opening dimension is the width of the hole in the wall, not of the fitted window. An axis dimension runs centre to centre and is what the structure uses. A clear dimension is the actual gap between two faces — the space you walk through.
Confusing them is the most common reason a door does not fit. When you write a dimension, be explicit about what it measures from and to.
What else belongs on a plan
- The name and area of every room.
- North, clearly drawn — without it you cannot discuss daylight.
- Door swing direction, shown with an arc.
- The section line, lettered at both ends (A–A), so the section has a reference.
- The scale, written out on the sheet: 'scale 1:50'. A misprinted plan with no written scale is unusable.
From 3D straight to a dimensioned plan
The advantage of a 3D model is that the plan is not drawn separately — it is cut. Slice the building at 1.2 m, below lintels and above sills, and you get exactly the wall and opening outlines.
In GrafitGo the cut comes out as vector SVG, with dimensions added automatically on selection, and prints to scale without pixelation. Change the model and re-cut the plan in two seconds instead of correcting a drawing.
At what height is a plan cut?
Conventionally 1.2 m above the floor. High enough to cut windows, low enough to miss the lintels.
Centimetres or millimetres?
In building work, centimetres on architectural plans and millimetres on details are usual. What matters is stating the unit once, clearly, and not mixing.
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