Blueprint Scale Converter

Convert between drawn and real-world lengths at any architectural scale, from 1/8" = 1' to metric 1:50.

How it works

Every drawing on a set of plans is drawn at a stated scale, a ratio between a length on the paper and the matching length in the real building. Architectural scales are written as a fraction of an inch standing in for a foot, like 1/4" = 1'-0", which means every 1/4 inch you measure on the sheet represents 1 foot on the actual wall. Engineering and civil drawings, and most drawings outside North America, use a ratio instead, like 1:50, where one unit drawn equals 50 of the same unit in real life. The calculator above does the multiplication either direction: give it a measured length on the page and a scale, and it returns the real dimension; give it a real dimension and it returns how long that should measure on the sheet.

Worked example: say you pull out an architect's scale and measure a wall on a 1/4" = 1'-0" floor plan at 3.5 inches. That scale has a factor of 48 (a quarter inch times 48 is 12 inches, one foot), so the real wall is 3.5 × 48 = 168 inches, which the tool reports as 14' 0". Flip it around and you get the same relationship in reverse: a wall you know is 14 feet long should measure 3.5 inches on that same sheet. On a metric drawing at 1:50, a 6 meter (600 cm) wall drawn to scale measures 12 cm on the page, since 600 divided by 50 is 12.

A caution worth repeating: only trust a measurement you take directly off the sheet with a scale ruler or architect's scale. Printed and scanned drawings get resized all the time, in a photocopier, a PDF export, or a home printer defaulting to "fit to page," and a resized sheet no longer measures true to its stated scale even though the scale note in the title block still says the original ratio.

FAQ

Why do architectural scales use fractions of an inch instead of a clean ratio?

It's historical convention in North American residential and commercial drawing sets. An architect's scale ruler is machined with several of these fraction-to-a-foot scales along its edges so a drafter can read real feet and inches directly off the paper without doing the multiplication by hand. Engineering scales and most international drawings use ratios instead because they're unit-agnostic, 1:50 works the same whether you're measuring in centimeters or inches.

What scale are most residential floor plans drawn at?

1/4" = 1'-0" is the most common scale for a full floor plan sheet, it fits an average house on a standard sheet size while staying readable. Larger detail drawings, like a kitchen or bathroom layout, often step up to 1/2" = 1'-0" or even 3/4" = 1'-0" so there's room to show cabinetry and fixtures clearly. Site plans go the other way, often 1/8" = 1'-0" or smaller, to fit the whole lot on one page.

Can I use this if the scale note just says "NTS"?

No. "NTS" means "not to scale," and it shows up on detail call-outs and diagrams where the drafter distorted proportions on purpose to make something clearer. A ruler measurement on an NTS drawing tells you nothing about real-world size, you need the written dimension instead.

Why does my measurement come out slightly different from the stated dimension on the drawing?

Small mismatches, an eighth of an inch or a centimeter or two, usually come down to line weight (the wall line itself has thickness) or a print that's been resized. If the gap is bigger than that, trust the printed dimension text over a ruler measurement every time, dimensions are the drafter's exact intent while a scaled measurement is always an approximation.

For more on how scale fits into the rest of a drawing, see Understanding Scale on Architectural Drawings, Drawing Scales and Line Weights Explained, and How to Read Dimensions on a Floor Plan.