Floor Plan Dimensions
Floor plan dimensions turn a drawing into something you can build or furnish from, but a figure such as 3600 or 11′-10″ can mean the floor you can carpet or the distance between wall centres. This guide explains how dimension lines work, how lengths are written in metric and imperial, which measurements a plan needs, and what each one is measured to.
Anatomy of a dimensioned plan
The parts of a dimension
A dimension has three parts. Extension lines run out from the two points being measured, with a small gap so they do not touch the drawing. The dimension line runs between them, ending in ticks, dots or arrowheads. The figure sits on or above the dimension line and gives the real length, whatever the scale of the drawing.
On a house plan dimensions are stacked in rows outside the walls: the overall length furthest out, a chain locating the interior walls inside that, and a row locating doors and windows closest to the building. Each inner chain should add up to the overall figure.
How lengths are written
Metric plans are usually dimensioned in millimeters without a unit, so 3600 means 3.6 m; some use meters to two decimals. Imperial plans use feet and inches, such as 11′-10″, where ′ means feet and ″ inches. A plan should say which unit it uses and stick to it.
Room sizes are usually written width first, as 3.6 × 4.2 m or 11′10″ × 13′9″, and areas in m² or sq ft.
Dimensioning a plan
Overall sizes first
Run the total length and width of the building along the outside of the plan.
Then the chains
Inside the overall line, a chain of dimensions locates each wall; the chain must add up to the overall size.
Locate the openings
Give each door and window a position from a corner or a wall, and its width.
Add room sizes
Label each room with its name and area, and its width and length where a reader needs them.
Keep them readable
Space dimension lines evenly, keep them off the drawing itself, and give each length only once.
Worked example: a two-room plan
In the drawing above, the overall dimension along the top is 5.40 m (17′9″). The chain inside it reads 3.00 m and 2.40 m, which locates the partition and adds up to the overall length. The side dimension gives the depth, 3.60 m (11′10″), so the living room is 3.0 × 3.6 m (10.8 m², 116 sq ft) and the bedroom 2.4 × 3.6 m (8.64 m², 93 sq ft).
Along the bottom, a third chain locates the window: 0.90 m from the corner, 1.20 m wide, then 0.90 m to the partition, again adding up to 3.00 m. Anyone ordering that window, or a blind for it, has every number they need without reaching for a ruler.
Centre lines, faces and clear sizes
A dimension can run to the centre of a wall, to its face, or between finished faces (the clear inside size). Each is useful, but mixing them on one drawing causes mistakes, so say which you use. Area figures vary the same way: a house’s quoted area may be measured to the outside of its walls, an apartment’s to the inside, and the rules for what counts differ between countries and markets.
MyFloorPlanMaker measures walls and rooms along wall centre lines. A room drawn 3.6 × 4.2 m between centre lines, with 150 mm walls, has a clear inside of about 3.45 × 4.05 m: its 15.1 m² (163 sq ft) is about 14.0 m² (150 sq ft) of actual floor. Allow for this when you order flooring.
Common dimensioning mistakes
Chains that do not add up
If 3000 + 2400 is written next to an overall 5500, one of them is wrong. Check every row.
The same length twice
Two figures for one distance drift apart when the plan changes. Give each length once.
Units left unstated
Is 36 inches or centimetres? State the unit in the title block.
Dimensions on top of the drawing
Figures crossing walls and furniture are easy to misread. Keep them outside or in clear floor.
Dimensions in the editor
Dimension tool
Press Shift+D, click two points, then click again to set how far the line sits from the wall.
Attached to corners
A dimension placed on corners follows the walls when you edit them.
Typed lengths
Type 3600, 3.6m or 11'10" while drawing a wall and press Enter.
Measure tool
Press M to check any distance and angle without adding anything to the plan.
Wall lengths on exports
PDF, SVG and printed plans can show every wall’s length.
Frequently asked questions
Which comes first in room dimensions, width or length?
Usually width then length, but conventions vary. If in doubt, read the dimension lines on the plan rather than the room label.
What does 12′-6″ mean on a floor plan?
Twelve feet six inches, which is 3.81 m.
Why do metric plans have no units on the dimensions?
By convention they are in millimeters, so 2400 means 2.4 m. The title block should say so; if it gives meters instead, figures are written with decimals, such as 2.40.
Are floor plan dimensions inside or outside the walls?
It depends on the drawing. Overall dimensions usually run to the outside faces; room dimensions may run to faces or to centre lines. The editor measures to centre lines.
How do I convert floor plan dimensions between feet and meters?
One foot is 0.3048 m and one inch is 25.4 mm. In the editor, switch the project’s units and every length converts; the square footage calculator converts areas.