Free tool
Architectural scale calculator: from drawing to real size, and back
Pick the scale, type what you measured the way it is written (3 1/2", 12'6" or 150 mm) and get the real size in feet and inches, decimal feet and meters, with the math shown. It also works in reverse and moves a measurement from one scale to another. Covers 11 architectural, 7 engineering and 8 metric scales. Free, nothing to sign up for.
By Camila BruggerFounder and CEO
Convert a measurement
Type it the way it is written: 3 1/2", 12'6", 1'-6 1/4", 2.35 in or 150 mm.
Reference
Architectural scale chart: every common scale and its factor
The scale factor is how many times larger the real object is than the drawing. Multiply a paper measurement by it to get the real size; divide a real size by it to get the length on paper. The last column says which drawings each scale is meant for (if you need a refresher on what each drawing type shows, see our guide to the types of architectural drawings).
Architectural scales
A fraction of an inch on paper equals one foot. Used for buildings: plans, elevations, sections and details.
Slide the table sideways to see every column.
| Scale | Factor | 1 in on paper | Typical drawings |
|---|---|---|---|
| 3" = 1'-0"1:4 | 4 | 4" | Details |
| 1 1/2" = 1'-0"1:8 | 8 | 8" | Details |
| 1" = 1'-0"1:12 | 12 | 1'-0" | Sections and details |
| 3/4" = 1'-0"1:16 | 16 | 1'-4" | Enlarged plans, sections and details |
| 1/2" = 1'-0"1:24 | 24 | 2'-0" | Enlarged plans, sections and details |
| 3/8" = 1'-0"1:32 | 32 | 2'-8" | Floor plans, elevations and enlarged plans |
| 1/4" = 1'-0"1:48 | 48 | 4'-0" | Floor plans, elevations, enlarged plans and sections |
| 3/16" = 1'-0"1:64 | 64 | 5'-4" | Floor plans and elevations |
| 1/8" = 1'-0"1:96 | 96 | 8'-0" | Floor plans, elevations and sections |
| 3/32" = 1'-0"1:128 | 128 | 10'-8" | Floor plans and elevations |
| 1/16" = 1'-0"1:192 | 192 | 16'-0" | Floor plans and elevations |
Engineering scales
One inch on paper equals a round number of feet, read in decimals. Used for site, grading, utility and landscape plans.
Slide the table sideways to see every column.
| Scale | Factor | 1 in on paper | Typical drawings |
|---|---|---|---|
| 1" = 10'-0"1:120 | 120 | 10'-0" | Site, grading, utility and landscape plans; plan and profile sheets |
| 1" = 20'-0"1:240 | 240 | 20'-0" | Site, grading, utility and landscape plans; plan and profile sheets |
| 1" = 30'-0"1:360 | 360 | 30'-0" | Site, grading, utility and landscape plans |
| 1" = 40'-0"1:480 | 480 | 40'-0" | Site, grading, utility and landscape plans |
| 1" = 50'-0"1:600 | 600 | 50'-0" | Site, grading, utility and landscape plans |
| 1" = 60'-0"1:720 | 720 | 60'-0" | Site, grading, utility and landscape plans |
| 1" = 100'-0"1:1200 | 1,200 | 100'-0" | Site, grading, utility and landscape plans |
Metric scales
A plain ratio: at 1:50, 1 mm on paper is 50 mm in reality. Watch the near misses: 1:50 is close to 1/4" = 1'-0" (1:48) but not the same.
Slide the table sideways to see every column.
| Scale | Factor | 1 cm on paper | Closest US scale | Typical drawings |
|---|---|---|---|---|
| 1:1 | 1 | 1 cm | Same in every system | Full size |
| 1:5 | 5 | 5 cm | 3" = 1'-0" (1:4) | Component and detail drawings |
| 1:10 | 10 | 10 cm | 1" = 1'-0" (1:12) | Component and detail drawings |
| 1:20 | 20 | 20 cm | 1/2" = 1'-0" (1:24) | Room plans and interior elevations |
| 1:50 | 50 | 50 cm | 1/4" = 1'-0" (1:48) | Floor plans, elevations and sections; room plans |
| 1:100 | 100 | 1 m | 1/8" = 1'-0" (1:96) | Floor plans, elevations and sections; site plans |
| 1:200 | 200 | 2 m | 1/16" = 1'-0" (1:192) | Site plans and sketch schemes |
| 1:500 | 500 | 5 m | 1" = 40'-0" (1:480) | Location and key plans |
Factors from Archtoolbox. Imperial uses from the drawing scale table in the Los Alamos National Laboratory CAD Standards Manual, which follows the US National CAD Standard; metric uses from First In Architecture.
How to use an architectural scale
1. Find the scale of that one drawing
Each view on a sheet carries its own scale, written under its title. A plan and a detail on the same sheet are usually at different scales, so read the note under the view you are measuring, not the one in the title block. If it says Scale: None or NTS, the drawing was not drawn to scale and measuring it tells you nothing.
2. Pick the matching edge
A triangular architect's scale has two scales on each edge that run in opposite directions, for example 1/4 from one end and 1/8 from the other. Use the row of numbers that starts at the zero on the end marked with your scale. The edge marked 16 is full size, in sixteenths of an inch.
3. Read whole feet, then the inches
Slide the scale until one end of the line sits on a whole foot mark and the other end falls inside the subdivided block past the zero. Read the feet at the first end and the inches in that block, then add them. At 1/4" = 1'-0", a line that covers 14 feet on the scale is 3 1/2 inches long on the paper.
4. Check it against a written dimension
Before you trust a measurement, scale one dimension that is already written on the sheet. If they match, the print is at scale. Written dimensions always govern: "Do not scale off dimensions" is a standard note on architects' drawings for exactly this reason.
No architect's scale at hand?
Any ruler in inches works. Measure the line, then multiply by the factor from the chart: 3 1/2" × 48 = 168" = 14'-0". With a metric ruler on a metric drawing it is the same move: 42 mm × 100 = 4,200 mm. The calculator above does both and shows the math.
Choosing a scale for a new drawing
Use the largest scale that fits the whole drawing on the sheet and still shows the detail it has to show. Keep every principal plan in a set at the same scale, and go up for enlarged plans of busy areas such as equipment rooms (1/4" = 1'-0" at least) and for congested sections and details (1/2" = 1'-0" at least). If your team sets view scales in Revit all day, keep our free Revit shortcuts sheet next to this one.
Before you measure a print
Printing a PDF? “Fit to page” breaks the scale
A drawing is only at scale on the paper size it was set up for, for example a 24 × 36 inch sheet. Print it on smaller paper with Fit or Shrink oversized pagesturned on, and Acrobat scales the whole sheet down to fit. A 24 × 36 sheet fitted onto 11 × 17 paper comes out at about 46% of full size, and smaller once the printer margins are taken, so a 1/4" = 1'-0" plan now reads at neither 1/4" nor 1/8". Every number you scale off it is wrong, and nothing on the page tells you.
- Print at Actual size or 100%on paper at least as large as the original sheet. Any "scale to fit" option gives an inaccurate print.
- Measure against the graphic scale (the scale bar) when you are not sure how a sheet was printed. It shrinks with the drawing, so it stays correct at any size. That is why drafting standards, such as the one at Los Alamos National Laboratory, ask for a general note on every scaled sheet telling readers to use the graphic scale if the print is not the original sheet size.
- Half size sets are the one clean exception.A 24 × 36 sheet printed at exactly 50% on 12 × 18 paper turns 1/4" = 1'-0" into 1/8" = 1'-0". Use the scale to scale mode above to get the new scale for anything else.
- Check a written dimension before you trust any measurement from a print.
The calculator reads drawings. Someone still has to draft them.
WorldTeams builds remote teams for US architecture, engineering and construction firms: vetted global talent working your hours, on your software, inside your workflow. That includes CAD drafters who turn markups into clean plans, sections and details at the scale your set calls for.
Questions, answered
How do you convert an architectural scale to real size?
Multiply the length you measure on the drawing by the scale factor. At 1/4" = 1'-0" the factor is 48, so 3 1/2 inches on paper is 3.5 × 48 = 168 inches, or 14'-0". To go the other way, divide the real length by the factor: a 25 foot wall is 300 ÷ 48 = 6 1/4 inches on the sheet. Any ruler works for this. The scale chart on this page lists the factor for every common scale.
What is the scale factor for 1/4 inch = 1 foot?
48. The factor is how many times bigger the real object is than the drawing: one foot is 12 inches, and 12 ÷ 1/4 = 48, so the ratio is 1:48. The same rule gives 96 for 1/8" = 1'-0", 24 for 1/2" = 1'-0" and 192 for 1/16" = 1'-0". Engineering scales work the same way: 1" = 20' is 20 × 12 = 240.
What is the difference between an architect's scale and an engineer's scale?
An architect's scale sets a fraction of an inch equal to one foot, like 1/4" = 1'-0", and reads in feet and inches. It is the one for buildings: plans, elevations, sections and details. An engineer's scale sets one inch equal to a round number of feet, like 1" = 20', and reads in decimals. It is the one for site, grading, utility and landscape plans. Read a site plan with the wrong one and you get a number that looks plausible and is wrong.
Is 1/4 inch scale the same as 1:50?
No. 1/4" = 1'-0" is 1:48, and 1:50 is about 4% smaller. The gap is easy to miss and it adds up: a 50 foot wall on a 1:50 drawing, measured with the 1/4" edge of an architect's scale, reads 48 feet. The same trap sits between 1/8" = 1'-0" (1:96) and 1:100. Check the scale noted under the drawing title before you pick up the ruler.
Why does my printed drawing not measure to scale?
Usually because the PDF was printed with Fit or Shrink oversized pages turned on, which resizes a large sheet to fit smaller paper. Print at Actual size or 100% on paper as large as the original sheet, or measure against the graphic scale bar, which shrinks along with the drawing. A print at exactly half size turns 1/4" = 1'-0" into 1/8" = 1'-0". Written dimensions always win over anything you measure.
What scale are floor plans drawn at?
Drafting standards based on the US National CAD Standard list floor plans and elevations from 1/16" to 3/8" = 1'-0", enlarged plans from 1/4" to 3/4" = 1'-0", and details at 1/2" = 1'-0" and larger. Within that range, pick the largest scale that fits the whole plan on the sheet and still shows the detail you need, and keep every principal plan in the set at the same scale.
Sources: Archtoolbox, CAD Scale Factors; Archtoolbox, Converting Between Drawing Scales; Archtoolbox, Free Printable Architect's Scale; Los Alamos National Laboratory, CAD Standards Manual, Section 200 (drawing scales per the National CAD Standard); First In Architecture, Understanding Scales and Scale Drawings; Santa Barbara City College via LibreTexts, Using an Architect's Scale Ruler; Adobe, Scale or resize printed pages in Acrobat and Reader; Wikipedia, Architectural drawing.
Last updated September 23, 2026.