What do the symbols on a floor plan mean?
A floor plan is full of lines that do not look like what they represent — a door is an arc, not a rectangle, and a thick line means something different from a thin one. Once you know the symbols, you can read a plan in a minute.
Short answer: most floor plans follow the same basic convention, whoever drew them: thick, filled lines are walls, a quarter circle with a line is a door and shows which way it swings, two parallel lines in a wall are a window, and a room name with a number beside it is the area in square metres. A dashed line usually means something that can't be seen directly — a hidden edge or a boundary between two layers.
Walls: thick lines, and what the thickness tells you
Walls are drawn as filled or hatched bands, thicker than every other line on the plan. The thickness isn't arbitrary — it shows the wall's actual dimension, so an insulated exterior wall looks wider than a thin partition. On a good plan you can therefore tell a thick exterior wall from a light partition just by looking at the line thickness, without reading a single number.
Doors: the arc shows which way it opens
A door is drawn as a gap in the wall line with a quarter-circle arc swinging out from the hinge side. The arc shows the door's swing direction — which way it opens — and how much space it needs when standing open. That's why a door on a floor plan takes up more room than the opening itself: the arc is part of the symbol, not decoration.
Note that a scan cannot always tell which way a door actually swings — it sees the opening, but not always the hinges. The swing direction is therefore often something you need to confirm or correct on the plan yourself.
Windows: two lines in a wall
A window is typically drawn as two or three parallel lines breaking the wall line — they mark the glass, set apart from the solid part of the wall on either side. The width of the symbol matches the window's actual width at the plan's scale.
Measurements: where the numbers sit, and what they measure
Dimension figures sit along a thin, often dashed reference line outside the wall itself, with small ticks or arrowheads marking exactly where the measurement starts and ends. Most plans measure in millimetres, even when a room is several metres long — that gives a more precise figure than centimetres, with no decimals. So always check the unit before comparing two figures from different plans.
Room names and areas
The room's name and its area in square metres usually sit in the middle of each room, often with two decimal places. The area is normally calculated from the internal measurement — the floor surface inside the walls, not including the walls' own thickness. It's worth checking, because an area measured to the wall's centreline can give a different — larger — figure than one measured internally.
Load-bearing walls — why they're often marked differently
Some plans mark load-bearing walls with a different hatch, colour or line style from ordinary partitions, to make them easy to spot. That's a useful marking to look for — but it isn't a guarantee. A plan can never establish with certainty whether a wall is load-bearing; that can only be determined on site by a building surveyor or an engineer who knows the building's construction.
What the symbols don't tell you
A floor plan shows where something stands — not what it's made of, how old it is, or whether it's legal. Two lines that look like an ordinary interior wall might actually conceal a chimney, a buried installation, or an earlier renovation that the plan never captured. The symbols are a shared code, not a full description of the building.
What does the scale ratio mean — 1:50, 1:100?
A figure like 1:50 tells you how many times reality has been scaled down on paper: one centimetre on the plan corresponds to 50 cm in real life. Construction drawings with lots of detail — door frames, material changes, a section through a wall — are often drawn at 1:50, while an overview plan of the whole house can get by with 1:100, where one centimetre equals a full metre. If you need to read off a measurement yourself with a ruler directly on the paper, it's therefore essential to know the scale ratio before you calculate anything further — the same line means something entirely different depending on the number in the corner.
Are there symbols for a chimney, a lift and a balcony?
Yes, and they follow the same logic as the other symbols: the shape hints at the function. A chimney is typically drawn as a filled-in square inside or against an exterior wall, because — unlike an ordinary wall — it's solid all the way through. A balcony or terrace is often marked as an area outside the house's actual exterior wall, set apart with a thinner line than the wall itself, because it isn't heated indoor space. A lift or a shaft is usually shown as a square with a cross or diagonal lines in it, to set it apart from an ordinary room you can walk into.
Why plans from different sources don't use quite the same symbols
There is no universal standard that every floor plan follows to the letter — the conventions have grown up across the industry, not been set by a single authority. So a plan from an architect, an app and an old set of construction drawings might well use slightly different symbols for the same thing, for example how a sliding door or a double door is shown. The basics — thick lines are walls, arcs are doors — hold true almost everywhere, but if you're unsure about a particular line, the quickest route is a legend on the plan itself, if there is one.
What HouseSense does
HouseSense's floor plans follow the same convention a builder or architect would recognise: walls as bands at their actual thickness, doors with a swing arc, windows as a break in the wall line, and room names with area. A legend on the plan itself explains the symbols, so a contractor can read it without having to ask what a given line means.
If you're unsure what a line on a specific plan represents — especially if it could be a load-bearing structure — always ask a building surveyor before you act on it.
How do you read a floor plan step by step?
- Find the scale ratio. Without it, you can't trust distances you measure yourself with a ruler on the paper.
- Find the north arrow. It tells you how the house is oriented relative to the world, not just relative to the paper.
- Follow the thick lines. They're the load-bearing and non-load-bearing walls that make up the house's basic shape.
- Find the breaks in the wall line. Arcs are doors, parallel lines in the wall are windows.
- Read the room names and areas. They give you the overview before you dig into individual measurements.
- Check the dimension figures last. That's where most errors in a quick read-through happen, because the unit — millimetres or centimetres — is easy to overlook.