How to read blueprints: the sheets, the scale, the symbols and the dimensions
Start with the title block for the sheet's name and scale, then read the floor plan: thick lines are walls, arcs are door swings, thin lines across a wall are windows, and the strings of numbers outside are the dimensions. On a 1/4 inch scale plan, every quarter inch on the paper is a foot on the house. Elevations show the outside, sections show it cut through, and schedules list the doors and windows.
Anthony Hicks30+ years in construction. Updated November 5, 2026.
Reading as
The sheets in a set
| Sheet | What it shows |
|---|---|
| Title or cover sheet | The project, the list of sheets, general notes |
| Site plan | The lot, the house on it, setbacks, driveways and utilities |
| Floor plans | Each floor from above, cut about 4 feet up: walls, doors, windows, stairs, rooms |
| Elevations | Each side of the house straight on: heights, roof, windows, siding |
| Sections | The house cut through: framing, floor and ceiling heights, the roof’s build-up |
| Details | Close-ups of how a part is built, at a larger scale |
| Schedules | Tables of the doors, windows and finishes, by mark |
| Trade sheets | Electrical, plumbing and mechanical plans |
The title block
Every sheet has a title block, usually in the lower right corner or along the right edge: the project, the sheet’s name and number, the date, the revisions, and the scale. Read it first; it says what you’re looking at and how big it is.
Reading the scale
The scale ties the paper to the house. On an architectural scale, 1/4” = 1’-0” means a quarter inch on the sheet is one foot on the building, a ratio of 1 to 48; 1/8” = 1’-0” is half that size, for bigger buildings. Site plans often use an engineer’s scale such as 1” = 20’.
Trust the written dimensions over a ruler: copies and PDFs get printed at the wrong size, and a sheet marked “not to scale” means exactly that.
Floor plan symbols
| What you see | What it is |
|---|---|
| Thick double lines | Walls, sometimes hatched or filled |
| An arc from a gap in a wall | A door, the arc showing which way it swings |
| Thin lines across a wall | A window, with its mark from the schedule |
| Parallel lines with an arrow and “UP” or “DN” | Stairs, the arrow pointing the way up or down |
| Dashed lines | Something overhead or hidden: a beam, cabinets above, the roof line |
| A circle with a letter or number | A mark pointing to a schedule, a section or a detail |
Dimensions
Dimensions run in strings outside the walls: the outer string is the building’s overall length, the next string in breaks it into wall segments and openings, and the inner strings locate the walls inside. They’re written in feet and inches (13’-7”), and may run to the face of the studs or to the finished wall; the plan’s notes say which.
No plans? Make one
A repair or restoration job may come with no drawings at all. BluMatrix draws the floor plan on the visit: a LiDAR scan of each room on an iPhone Pro, or the corners marked on any phone, with every wall’s length, the ceiling height, and the doors and windows, drawn to size and carried into the estimate. The guide to measuring a room covers doing it by hand.
Common questions
Why are they called blueprints?
The name comes from an old copying process that made white lines on blue paper. Drawings today are printed black on white or sent as PDFs, but the name stuck.
What scale are house plans?
Floor plans for houses are usually 1/4” = 1’-0”; larger buildings use 1/8” = 1’-0”; details go up to 1 1/2” or 3” = 1’-0”.
How do I find a room’s size on a blueprint?
Read the dimension strings along its walls, or the room’s label, which often gives its size, such as 12’-0” × 14’-0”. Multiply for the floor area; the square footage calculator adds up odd shapes.