Drawing scales
Every drawing scale, explained.
What each architectural, engineering and metric scale means, the ratio behind it, and conversion tables in both directions.
A drawing scale says how much smaller the drawing is than the real thing. 1/4" = 1'-0" means a quarter inch on paper is one foot in reality, a ratio of 1:48. To convert, multiply what you measure on paper by the ratio. Need to convert a number now? Use the scale converter.
Architectural scales
Used for floor plans, elevations and details in the US. Written as inches on paper = 1 foot.
| Scale | Ratio | 1 inch on paper | Typical use |
|---|---|---|---|
| 1/16" = 1'-0" | 1:192 | 16 ft | Used for overall plans of large buildings and small site plans. |
| 3/32" = 1'-0" | 1:128 | 10.67 ft | Used for floor plans of large buildings that won't fit at 1/8 inch. |
| 1/8" = 1'-0" | 1:96 | 8 ft | Used for floor plans of large homes and commercial buildings, and for key plans. |
| 3/16" = 1'-0" | 1:64 | 5.33 ft | Used for residential plans that are too big for the sheet at 1/4 inch. |
| 1/4" = 1'-0" | 1:48 | 4 ft | The standard scale for house floor plans and elevations in the US. |
| 3/8" = 1'-0" | 1:32 | 2.67 ft | Used for enlarged plans and interior elevations. |
| 1/2" = 1'-0" | 1:24 | 2 ft | Used for enlarged kitchen and bath plans and interior elevations. |
| 3/4" = 1'-0" | 1:16 | 1.33 ft | Used for cabinet elevations and construction details. |
| 1" = 1'-0" | 1:12 | 1 ft | Used for construction details. |
| 1-1/2" = 1'-0" | 1:8 | 0.67 ft | Used for large construction details such as stairs and millwork. |
| 3" = 1'-0" | 1:4 | 0.33 ft | Used for full-detail sections of trim, framing and connections. |
Engineering scales
Used for site plans and civil drawings. Written as 1 inch = so many feet.
| Scale | Ratio | 1 inch on paper | Typical use |
|---|---|---|---|
| 1" = 10' | 1:120 | 10 ft | An engineering scale used for small site plans and detailed civil drawings. |
| 1" = 20' | 1:240 | 20 ft | An engineering scale used for residential site plans and plot plans. |
| 1" = 30' | 1:360 | 30 ft | An engineering scale used for larger lots and site plans. |
| 1" = 40' | 1:480 | 40 ft | An engineering scale used for subdivision and large site plans. |
| 1" = 50' | 1:600 | 50 ft | An engineering scale used for large sites and grading plans. |
| 1" = 100' | 1:1200 | 100 ft | An engineering scale used for area maps and large developments. |
Metric scales
Used everywhere else. Written as a ratio: 1:100 means 1 mm on paper is 100 mm in real life.
| Scale | Ratio | 1 cm on paper | Typical use |
|---|---|---|---|
| 1:20 | 1:20 | 0.2 m | A metric scale used for details and enlarged plans. |
| 1:50 | 1:50 | 0.5 m | A metric scale used for detailed floor plans and room layouts. |
| 1:100 | 1:100 | 1 m | The standard metric scale for house floor plans, sections and elevations. |
| 1:200 | 1:200 | 2 m | A metric scale used for plans of large buildings and small site plans. |
| 1:500 | 1:500 | 5 m | A metric scale used for site and location plans. |
Let the plan tell you its scale.
Open a PDF plan in FloorFigures and it reads the printed dimensions, finds the real scale and warns you if the scale note is wrong. Free.