What does 1/4 inch scale mean?

On a drawing at 1/4" = 1'-0", every quarter inch on paper stands for one foot in real life. That's a ratio of 1:48, so 1 inch on paper is 4 feet. A wall that measures 3 1/2 inches on the sheet is 3.5 × 4 = 14 feet long.

How do I convert 1/8 inch scale to feet?

Multiply the inches measured on paper by 8. At 1/8" = 1'-0" (1:96), 1 inch on paper is 8 feet, so 2 1/4 inches on paper is 2.25 × 8 = 18 feet. To go the other way, divide feet by 8 to get inches on paper.

Is 1/4 inch scale the same as 1:50?

No. 1/4" = 1'-0" is exactly 1:48. 1:50 is a metric scale, and it's about 4% smaller. If you measure a 1:50 drawing with a 1/4 inch scale ruler, every length comes out about 4% short, which is enough to matter for areas and material orders.

How do I find the scale of a drawing?

Measure a printed dimension on the sheet, such as a wall labeled 10'-0", and divide the real length by the paper length in the same units. If 10 feet (120 inches) measures 2 1/2 inches on paper, the ratio is 120 ÷ 2.5 = 48, so the drawing is 1:48, or 1/4" = 1'-0". Check a second dimension to confirm.

What does 1 inch = 20 feet mean on a site plan?

It's an engineering scale: each inch on paper is 20 feet on the ground, a ratio of 1:240 (20 feet is 240 inches). A lot line measuring 4.5 inches on the plan is 4.5 × 20 = 90 feet. It's often confused with 1:20, which is a much larger metric detail scale.

Free calculator

Drawing Scale Converter: Inches on Paper to Feet

Free scale converter for architectural, engineering and metric drawings: 1/4" = 1', 1/8" = 1', 1:100 and more, both directions.

Drawing scale

Length on paper

Inches; fractions work: 3 1/2, 3-1/2 or 3.5.

Result

Real length

14.00ft

14' 0"

Scale: 1/4" = 1'-0" (1:48)
On paper: 3 1/2 in
1 in on paper equals: 4.00 ft

Only measure a printout or PDF at its original size. Printing with 'fit to page' changes every length on the sheet.

How it's calculated

Real length = length on paper × the scale ratio. At 1/4" = 1'-0" the ratio is 1:48, so 1 inch on paper is 4 ft, and 3 1/2 in on paper is 14 ft. At 1:100, 45 mm on paper is 4.5 m. To go from real to paper, divide by the ratio instead.

How to use the scale converter

To real turns a length measured on the drawing into a real length: pick the scale, then type the paper measurement in inches (fractions like 3 1/2 work) or millimeters for metric scales. To paper does the reverse, which helps when you're drawing to scale. Find scale works out the scale from a dimension printed on the drawing: measure it on paper, enter the real length, and the calculator gives the ratio and the nearest standard scale. For a scale that isn't listed, choose Custom 1:N.

The math behind drawing scales

Every scale is a ratio of real size to drawing size. Architectural scales are written as paper inches per foot: 1/4" = 1'-0" means a quarter inch for every 12 inches, and 12 ÷ 0.25 = 48, so the ratio is 1:48. Engineering scales give feet per inch: 1" = 20' is 240 inches per inch, or 1:240, not 1:20. Metric scales are already ratios: at 1:100, 1 mm on paper is 100 mm (10 cm) in reality.

Similar-looking scales aren't interchangeable. 1/4" = 1'-0" (1:48) and 1:50 differ by about 4%, and 1/8" = 1'-0" (1:96) and 1:100 by about 4% too. Measure a drawing with the wrong one and every length is off by that much, and every area by about twice that.

Every standard drawing scale

Scale	Ratio	1 unit on paper	Type	Typical use
1/16" = 1'-0"	1:192	1 in = 16' 0"	Architectural	Used for overall plans of large buildings and small site plans.
3/32" = 1'-0"	1:128	1 in = 10' 8"	Architectural	Used for floor plans of large buildings that won't fit at 1/8 inch.
1/8" = 1'-0"	1:96	1 in = 8' 0"	Architectural	Used for floor plans of large homes and commercial buildings, and for key plans.
3/16" = 1'-0"	1:64	1 in = 5' 4"	Architectural	Used for residential plans that are too big for the sheet at 1/4 inch.
1/4" = 1'-0"	1:48	1 in = 4' 0"	Architectural	The standard scale for house floor plans and elevations in the US.
3/8" = 1'-0"	1:32	1 in = 2' 8"	Architectural	Used for enlarged plans and interior elevations.
1/2" = 1'-0"	1:24	1 in = 2' 0"	Architectural	Used for enlarged kitchen and bath plans and interior elevations.
3/4" = 1'-0"	1:16	1 in = 1' 4"	Architectural	Used for cabinet elevations and construction details.
1" = 1'-0"	1:12	1 in = 1' 0"	Architectural	Used for construction details.
1-1/2" = 1'-0"	1:8	1 in = 8"	Architectural	Used for large construction details such as stairs and millwork.
3" = 1'-0"	1:4	1 in = 4"	Architectural	Used for full-detail sections of trim, framing and connections.
1" = 10'	1:120	1 in = 10' 0"	Engineering	An engineering scale used for small site plans and detailed civil drawings.
1" = 20'	1:240	1 in = 20' 0"	Engineering	An engineering scale used for residential site plans and plot plans.
1" = 30'	1:360	1 in = 30' 0"	Engineering	An engineering scale used for larger lots and site plans.
1" = 40'	1:480	1 in = 40' 0"	Engineering	An engineering scale used for subdivision and large site plans.
1" = 50'	1:600	1 in = 50' 0"	Engineering	An engineering scale used for large sites and grading plans.
1" = 100'	1:1200	1 in = 100' 0"	Engineering	An engineering scale used for area maps and large developments.
1:20	1:20	1 cm = 0.2 m	Metric	A metric scale used for details and enlarged plans.
1:50	1:50	1 cm = 0.5 m	Metric	A metric scale used for detailed floor plans and room layouts.
1:100	1:100	1 cm = 1 m	Metric	The standard metric scale for house floor plans, sections and elevations.
1:200	1:200	1 cm = 2 m	Metric	A metric scale used for plans of large buildings and small site plans.
1:500	1:500	1 cm = 5 m	Metric	A metric scale used for site and location plans.

Scaling a PDF without a ruler

For PDFs, FloorFigures finds the scale for you, free. It reads printed dimension strings and scale notes such as 1/4" = 1'-0" or 1:100, and warns when the note disagrees with the dimensions, which is the sign of a resized PDF. For images, click both ends of any known length to set the scale. The PDF scaling guide covers both.

Updated October 12, 2026 · FloorFigures

Questions

What does 1/4 inch scale mean?: On a drawing at 1/4" = 1'-0", every quarter inch on paper stands for one foot in real life. That's a ratio of 1:48, so 1 inch on paper is 4 feet. A wall that measures 3 1/2 inches on the sheet is 3.5 × 4 = 14 feet long.
How do I convert 1/8 inch scale to feet?: Multiply the inches measured on paper by 8. At 1/8" = 1'-0" (1:96), 1 inch on paper is 8 feet, so 2 1/4 inches on paper is 2.25 × 8 = 18 feet. To go the other way, divide feet by 8 to get inches on paper.
Is 1/4 inch scale the same as 1:50?: No. 1/4" = 1'-0" is exactly 1:48. 1:50 is a metric scale, and it's about 4% smaller. If you measure a 1:50 drawing with a 1/4 inch scale ruler, every length comes out about 4% short, which is enough to matter for areas and material orders.
How do I find the scale of a drawing?: Measure a printed dimension on the sheet, such as a wall labeled 10'-0", and divide the real length by the paper length in the same units. If 10 feet (120 inches) measures 2 1/2 inches on paper, the ratio is 120 ÷ 2.5 = 48, so the drawing is 1:48, or 1/4" = 1'-0". Check a second dimension to confirm.
What does 1 inch = 20 feet mean on a site plan?: It's an engineering scale: each inch on paper is 20 feet on the ground, a ratio of 1:240 (20 feet is 240 inches). A lot line measuring 4.5 inches on the plan is 4.5 × 20 = 90 feet. It's often confused with 1:20, which is a much larger metric detail scale.

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