Guide
How to Read Floor Plan Dimensions and Scale
What 12'-6" means, which dimensions are to wall faces versus centers, and how to tell what scale your floor plan is drawn at.
Updated · FloorFigures
Short answer
Dimensions are written in feet and inches as 12'-6" (12 feet 6 inches), or in millimeters on metric plans (3600 = 3.6 m). A room label like 12'-4" × 13'-4" is the room's inside width and length, and the plan's notes say whether walls are dimensioned to their faces or centerlines. The scale is in the title block (1/4" = 1'-0" is 1:48); check it by measuring a printed dimension.
A floor plan has two kinds of numbers: written dimensions, which are exact, and the drawing itself, which is only as accurate as its scale. Reading the dimensions correctly, and knowing what they're measured to, is most of the job. Here's the notation, how dimension strings work, and how to work out a plan's scale.
What does 12'-6" mean?
Twelve feet, six inches. The single mark is feet, the double mark is inches, and the dash just separates them. Metric plans usually give dimensions in millimeters without writing the unit, so 3600 is 3,600 mm, or 3.6 m.
| Written | Means | As a decimal |
|---|---|---|
| 12'-6" | 12 feet 6 inches | 12.5 ft |
| 12' 6" or 12'6" | The same, without the dash | 12.5 ft |
| 5'-3 1/2" | 5 feet 3-1/2 inches | 5.29 ft |
| 0'-9" or 9" | 9 inches | 0.75 ft |
| 12.5' | 12.5 feet (decimal feet, common on site plans) | 12.5 ft |
| 3600 | 3,600 mm on a metric plan | 3.6 m |
The trap is converting inches to decimals. Inches are twelfths of a foot, not tenths, so 12'-4" is 12.33 ft, not 12.4.
| Inches | 1 | 2 | 3 | 4 | 6 | 8 | 9 | 10 |
|---|---|---|---|---|---|---|---|---|
| Feet | 0.083 | 0.167 | 0.25 | 0.333 | 0.5 | 0.667 | 0.75 | 0.833 |
How do strings of dimensions work?
Dimensions are drawn as a line with a mark at each end (a tick, arrow or dot) and the length written along it. Thin extension lines run from the dimension line to the wall or opening it measures. Several dimensions in a row along one side form a string, and the strings are layered: the outermost gives the overall length, and the inner ones locate walls, corners, doors and windows.
The parts of a string should add up to the overall dimension. That's a quick check on any plan:
| Segment | Length | In feet |
|---|---|---|
| Wall to window | 3'-6" | 3.5 |
| Living room | 12'-0" | 12.0 |
| Hall | 3'-0" | 3.0 |
| Kitchen | 14'-6" | 14.5 |
| Overall | 33'-0" | 33.0 |
If a string doesn't add up to its overall, one of the numbers is wrong. Ask whoever drew the plan, or check against a wall you can measure.
Overall dimensions vs room dimensions
Overall dimensions run around the outside of the building and measure the whole footprint. Room dimensions are inside, from one wall surface to the opposite one. The difference between them is the walls. A wall framed with 2×4 studs is 3-1/2 inches of framing, about 4-1/2 inches with drywall on both sides; exterior walls are thicker. That's why room sizes always add up to less than the house: see how to calculate square footage from a floor plan.
Are dimensions to the wall face or the centerline?
Both conventions exist. Some plans dimension to the face of the framing, some to the finished wall surface, and some to the centerline of each wall; doors and windows are often located by their centerlines. The plan's general notes usually say which, in a line such as "dimensions are to face of stud unless noted otherwise." It matters when you need the finished room size:
| Dimensioned to | What it measures | A room dimensioned 12' × 14' is finished at about |
|---|---|---|
| Face of finish | The wall surface you see | 12' × 14' (168 sq ft) |
| Face of stud | The framing, before drywall | 11'-11" × 13'-11" (166 sq ft) |
| Centerline | The middle of each wall | 11'-7 1/2" × 13'-7 1/2" (158 sq ft) |
The face-of-stud and centerline rows assume 1/2-inch drywall and 2×4 interior walls. On a centerline plan, a 12' × 14' room loses about 6% of its floor area to the walls. For a house's total square footage, none of this applies: ANSI Z765 measures to the exterior finished surface of the outside walls. See ANSI Z765.
What does a room label like 12'-4" × 13'-4" mean?
It's the room's inside width and length, wall face to wall face. Builder and marketing plans often round these and measure to the widest points, and they usually leave out closets. The order of the two numbers varies, so check it against the drawing. For area, convert the inches correctly:
| Method | Math | Area |
|---|---|---|
| Correct | 12.333 × 13.333 | 164.4 sq ft |
| Inches read as tenths (wrong) | 12.4 × 13.4 | 166.2 sq ft |
On an L-shaped or angled room, a single label can only describe a rectangle, usually the main part of the room. Measure the actual shape for flooring, as in L-shaped and irregular rooms. For listings, see room dimensions for the MLS.
Common door and window symbols
| Symbol | What it is |
|---|---|
| A gap in the wall with a quarter-circle arc | A swinging door; the arc shows which way it opens |
| Two arcs meeting in the middle | A pair of doors (double or French doors) |
| Two thin overlapping lines in the opening | Sliding or bypass doors |
| A door line running into the wall | A pocket door |
| Thin parallel lines across the wall thickness | A window |
| A code like 3068 or 2868 | A door size: 3'-0" × 6'-8" or 2'-8" × 6'-8" |
| Dashed lines | Something overhead, such as upper cabinets, a beam or an opening above |
Window sizes often use a similar width-then-height code, but manufacturers' codes vary, so check the window schedule if the plan has one.
What scale is my floor plan?
Look for the scale note first: it's in the title block or just under the drawing title, for example SCALE: 1/4" = 1'-0". A sheet can carry drawings at different scales, so read the one under the drawing you're measuring. "NTS" means not to scale. A graphic scale bar is the most reliable marker, because it shrinks or grows along with the drawing.
If there's no note, or the plan might have been printed or exported at a different size, work it out:
- Measure a long printed dimension on the paper, in inches.
- Convert the real length to inches. 16'-0" is 192 in.
- Divide real by measured. If 16'-0" measures 4 in, 192 ÷ 4 = 48: the plan is 1:48, which is 1/4" = 1'-0".
- Find the result in the table below. If it's far from every standard scale (say 1:61), the plan was resized: use the ratio you measured instead. How to scale a PDF drawing explains why.
| Scale | Ratio | On paper | Common use |
|---|---|---|---|
| 1/8" = 1'-0" | 1:96 | 1 in = 8'-0" | Floor plans of large homes and commercial buildings, and for key plans |
| 3/16" = 1'-0" | 1:64 | 1 in = 5'-4" | Residential plans that are too big for the sheet at 1/4 inch |
| 1/4" = 1'-0" | 1:48 | 1 in = 4'-0" | Standard scale for house floor plans and elevations in the US |
| 1/2" = 1'-0" | 1:24 | 1 in = 2'-0" | Enlarged kitchen and bath plans and interior elevations |
| 1" = 10' | 1:120 | 1 in = 10'-0" | Small site plans and detailed civil drawings |
| 1" = 20' | 1:240 | 1 in = 20'-0" | Residential site plans and plot plans |
| 1:50 | 1:50 | 1 cm = 0.5 m | Detailed floor plans and room layouts |
| 1:100 | 1:100 | 1 cm = 1 m | Standard metric scale for house floor plans, sections and elevations |
| 1:200 | 1:200 | 1 cm = 2 m | Plans of large buildings and small site plans |
US house plans are most often 1/4" or 1/8" scale, site plans use engineering scales such as 1" = 20', and metric house plans are commonly 1:100 or 1:50. The full list is under drawing scales, and the scale converter turns paper measurements into real ones.
Reading a plan in FloorFigures
FloorFigures does this reading for you on PDF plans. It's free and runs in your browser. It reads dimension strings such as 12'-6", 3600 and 3.6 m and scale notes such as 1/4" = 1'-0" and 1:100, sets the scale from them, and warns you when a scale note disagrees with the dimensions. Rooms you trace on a PDF are named from the plan's text. On a scan or photo, which has no text it can read, click both ends of a printed dimension and type it in.
Questions
- What does 12'-6" mean on a floor plan?
- It means 12 feet 6 inches, or 12.5 ft. The single mark (') is feet, the double mark (") is inches, and the dash only separates them; it isn't a minus sign. You'll also see it written 12' 6" or 12'6".
- Which number comes first in room dimensions?
- There's no universal rule. Many plans give width first, but drafters vary, so check the label against the drawing or the dimension strings around the room. For the area it doesn't matter: a room labeled 12'-4" × 13'-4" is 164 sq ft either way.
- Are floor plan dimensions inside or outside measurements?
- Both appear on the same plan. Room size labels are inside measurements, wall to wall. Overall dimensions run around the outside of the building. Dimension strings that locate walls can be to the wall faces or to their centerlines, and the plan's general notes say which.
- How can I tell what scale my floor plan is?
- Read the scale note in the title block or under the drawing title, such as 1/4" = 1'-0" (1:48) or 1:100. To check it, or if there's no note, measure a printed dimension in inches, convert the real length to inches, and divide the real length by the measured length. A result near 48 means 1/4-inch scale; near 96 means 1/8-inch scale. A result that matches no standard scale means the plan was resized, so use the ratio you measured.
- What does NTS mean on a plan?
- NTS means not to scale. The drawing is a diagram, so you can't measure it with a ruler; use only the written dimensions. A plan marked NTS can still be measured in software if it has enough printed dimensions to set a scale from, but check several of them, because a diagram may not be drawn in proportion.
- How do I convert inches to decimal feet?
- Divide the inches by 12: 3 in is 0.25 ft, 4 in is 0.333 ft, 6 in is 0.5 ft and 9 in is 0.75 ft. So 12'-4" is 12.33 ft, not 12.4 ft. Using 12.4 by mistake on a 12'-4" × 13'-4" room gives 166 sq ft instead of 164.