How to read a floor plan: scale, dimensions and symbols
A floor plan is a drawing of one level of a house as if it were cut horizontally about 4 feet above the floor and seen from above. Once you know how to read the scale, the dimension strings and a dozen symbols, almost any residential plan makes sense. Here is what to look at, in the order that helps most.
Updated 2026-10-19. Drafting conventions vary a little between offices. When a plan has a legend or a symbol sheet, it wins over any general guide, this one included.
Start with the title block, scale and north arrow
The title block, usually in a corner or along one edge, names the property, the sheet, the date and who drew it. Near it you will find the scale. US house plans are most often drawn at 1/4 inch = 1 foot, so one inch on the paper is four feet in the house; 1/8 inch = 1 foot is common for larger buildings and site plans. A scale is only true when the sheet is printed at its intended size, so read the written dimensions rather than measuring the paper. A north arrow tells you which way the house faces, which matters for light and for matching the plan to the street.
Reading dimensions
- Feet and inches. Plans write lengths like 12'6", meaning 12 feet 6 inches. The single mark is feet, the double mark is inches.
- Dimension strings. Lines with ticks or arrows at each end, usually outside the walls, give the distance between two points. The outer string is the overall size of the house; inner strings break it into rooms, walls and openings.
- Room labels. A label such as BEDROOM 11'0" x 12'6" gives the room's two sizes, usually measured between the wall surfaces. Which number is the width varies, so check it against the dimension strings.
- Where dimensions point. Some plans dimension to the face of a wall, others to the center of the wall or the face of the framing. A note or the way the ticks line up tells you which.
Common floor plan symbols
| What you see | What it means |
|---|---|
| Thick double lines, sometimes filled | Walls. Exterior walls are usually drawn thicker than interior ones. |
| A gap in a wall with a thin line and a quarter circle arc | A swinging door. The arc shows which way it opens and the side the hinges are on. |
| Parallel lines sliding past each other inside an opening | A sliding or pocket door. |
| Thin lines inside the wall thickness | A window. A tag or a schedule gives its size. |
| A row of parallel lines with an arrow and UP or DN | Stairs, with the direction you travel from this floor. |
| Dashed lines | Something above the cut or hidden: upper cabinets, a beam, an attic opening or a roof edge. |
| Simple outlines of a tub, toilet, sink or range | Plumbing fixtures and appliances, drawn to their real size. |
| Small circles and letters on walls and ceilings | Electrical outlets, switches and lights. A legend on the electrical sheet explains them. |
| A circle with a number and a letter, or an arrow with a sheet number | A reference to a detail, section or elevation on another sheet. |
Three checks that catch most misreadings
- Add up the strings. The room and wall dimensions along one side should add up to the overall dimension on that side. If they do not, one number is wrong.
- Walk the plan. Start at the front door and trace how you would move through the house. Doors that open into each other, or a hallway narrower than you expected, show up quickly.
- Match it to the house. Pick two or three rooms and measure them. An old plan may show the house as designed, not as built; see as-built vs measured survey drawings.
What a floor plan does not show
A floor plan shows the layout of one level. Heights are on elevations and sections, beams and joists are on framing plans, and the lot, setbacks and property lines are on a site plan. When a project touches any of those, ask for the matching sheet rather than reading it off the floor plan.
Where we fit
We draw the existing floor plan of your home from your measurements and photos, with dimension strings and room sizes laid out the way described above, so you and your contractor read the same numbers. The first plan is free with FIRSTPLAN and each extra plan is $10.
Free first 2D floor plan
New customers get one 2D floor plan of one floor of their home free, one per new customer. Use the code FIRSTPLAN on the quote form.
- What you send: the room measurements of that floor (a hand sketch with numbers is fine) and photos of each room.
- What you get: an as-built 2D floor plan of that floor as a PDF, drawn from your measurements.
- When: usually within 5 US business days after we have your measurements and photos. If we are behind, we tell you the date before we start.
- No card, nothing to pay, no obligation to order anything else.
- More plans: first plan free with FIRSTPLAN, each extra plan $10 (another floor or another property).
A floor plan drawn from your measurements is a record of the rooms you measured. It does not certify the structure or the lot, and it is no substitute for a survey or for engineered drawings.