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How to Scale a Floor Plan: Resize a Drawing or Calibrate an Image

To scale a floor plan, decide how many real feet one inch on the sheet stands for, then draw, resize, or calibrate to that ratio. US residential plans use 1/4″ = 1′ (1:48); metric plans use 1:50. To change the scale of a plan you already have, multiply by a scale factor, which is the new scale divided by the old one. To make a photo or PDF measurable, calibrate it from one wall you know.

Three different jobs hide behind the phrase, depending on who is asking: picking a scale before you draw, converting a finished drawing to a new scale, and telling software what one pixel of an image is worth. All three are below. This page belongs to our guide to floor plan measurement tools.

What scaling a floor plan means

A floor plan is a scaled drawing. Every distance on the sheet is the real distance divided by the same number, and that number is the scale. At 1/4″ = 1′ a 20-foot wall is 5 inches on paper. The ratio form is 1:48, because 12 inches times 4 is 48. A drawing is "to scale" when that one ratio holds everywhere on the sheet, which what a to-scale floor plan means goes into in more depth.

Drawing to scale means choosing a ratio before you start so the plan fits the sheet and reads clearly. Rescaling means enlarging or reducing an existing plan to a different ratio without distorting it. Calibrating means giving software one known length so a photo or PDF measures in feet or meters.

1. Choose a scale for a floor plan you are drawing

Pick the largest scale that fits the whole floor on your sheet and still leaves room for dimension strings around it. A larger scale gives you more detail per foot, which is why 1/4″ = 1′ is the residential standard and the smaller ratios are compromises for sheet size.

A 60 by 40 foot house at 1/4″ = 1′ is 15 by 10 inches, so it fits a 24 × 36 sheet with plenty of margin. At 1/8″ = 1′ the same house is 7.5 by 5 inches and fits letter paper. Graph paper with a 1/4-inch grid makes the choice for you: one square is one foot, and you are at 1/4″ = 1′ without doing any math. Our guide to drawing a floor plan by hand walks through that setup.

2. Scale a floor plan up or down with a scale factor

Divide the new scale by the old one. That number is the scale factor, and it is the percentage you type into a copier, a PDF print dialog, or a CAD scale command.

• 1/8″ = 1′ up to 1/4″ = 1′: (1/4) ÷ (1/8) = 2, so enlarge to 200 percent.
• 1/4″ = 1′ down to 1/8″ = 1′: the factor is 0.5, so reduce to 50 percent.
• 1/4″ = 1′ down to 3/16″ = 1′: 0.75, so 75 percent.
• 3/16″ = 1′ up to 1/4″ = 1′: 1.33, so 133 percent.
• 1:100 up to 1:50: 100 ÷ 50 = 2, so 200 percent.

Scale the drawing uniformly. Stretching it in one direction throws off every angle and area. And leave the dimension text alone: a wall labeled 12′-6″ is still 12′-6″ after you enlarge the sheet, only the line under it got longer. In CAD, scale the geometry and let annotative text keep its size. On paper, write the new scale in the title block so the next person is not misled.

Converting between ratio and fraction notation, or between imperial and metric, is quicker with our floor plan scale calculator.

3. Print a floor plan to scale

A lot of "to scale" printouts are not, because the print dialog shrank them without saying so. To print at true scale:

1. Set page scaling to 100 percent or actual size, and turn off fit to page, shrink to fit, and fit to printable area.
2. Pick a paper size the drawing fits at that scale. A 24 × 36 plan will not fit letter paper at 100 percent. If you have to print it small, accept the new scale and label it.
3. Print one sheet and put a ruler on it. A wall labeled 20′-0″ should measure 5 inches at 1/4″ = 1′, and a scale bar should measure what it says.
4. If the scale you verified differs from the title block, write it on the sheet.

4. Scale a floor plan image or PDF so it measures true

A photo, a scan, or a listing PDF has no scale you can trust, even when the title block states one, because the file has almost always been resized somewhere along the way. So instead of reading the printed ratio, calibrate: give a measurement tool one real length and let it work out the rest.

1. Upload the plan to MeasureFloorPlan or another measurement tool.
2. Find one length you know. A labeled wall is best, then a scale bar, then an overall width from county records, and a standard 36-inch door opening if nothing is printed.
3. Click both ends of that length on the plan and type the real distance.
4. The tool divides pixels by feet and applies that ratio to the whole image. Every wall and room you trace afterward reads in real units.

There is no ratio to look up or type. Which wall to pick, and why click error shrinks with a longer reference, is in how to set scale on a floor plan tool. If you would rather work the scale out by hand first, see how to determine the scale of a floor plan.

5. Scale a hand-drawn sketch

Field sketches are rarely to scale. They carry the measurements as written numbers instead. To turn one into a scaled plan, pick a scale from the table above and redraw each wall at its measured length times the scale; on 1/4-inch graph paper a 14-foot wall is 14 squares. Or skip the redraw: photograph the sketch, upload it, and calibrate from any wall you wrote a length on, as in step 4. Either way, take room sizes from the written numbers rather than the traced shapes, because the proportions of a rough sketch are off.

How to check that a floor plan is scaled correctly

• Measure a second labeled wall. After scaling by any method, a wall you did not use as the reference should read within an inch or two of its label.
• Look at the doors. Interior doors come out between 2.5 and 3 feet on a correctly scaled plan. A 5-foot door means the scale is off by about double.
• Compare the total to the listed area. Interior wall-to-wall square footage runs 5 to 10 percent under the listed gross living area, because ANSI Z765 measures to the outside of exterior walls. A 30 percent gap is a scale problem.

Area errors are roughly double the scale error, so a reference that is 3 percent off gives square footage about 6 percent off. Wikipedia's pages on scale ratios and architectural drawing cover the background, and floor plan scale explained covers reading and converting the notation itself.

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