Font Size Calculator Online

Choose a readable font size for the way people will read

A font size that works on a phone held in your hand can be too small on a sign across a room. Viewing distance changes how large letters appear to the reader, even when the lettering itself stays the same. Use this font size calculator to estimate how tall the letters should be for a particular distance, text type, and lighting condition. The result gives you a starting size to try in your layout.

The calculator reports x-height, font size, and visual angle. The x-height is the height of a lowercase x. It represents the main body of many lowercase letters, without the taller strokes of letters such as h or the tails of letters such as p. Font size is the setting you enter in a design tool. Two fonts set to the same size can have different x-heights, which is why one may look noticeably smaller.

How to use the font size calculator

1. Choose the closest preset. The calculator starts with Book, magazine and uses a 40 cm reading distance.
2. Enter the distance from the reader's eyes to the text in centimeters. You can also use the slider beneath the visual-angle diagram.
3. Choose a text type and lighting condition. If the same layout will be read in different settings, calculate a second result for the less favorable setting and compare.
4. Enter the x-height ratio for the font if you know it. For screen presets, enter the effective pixel density of the display setup when you have a measured value.
5. Apply the suggested size to the intended font. Check a real paragraph, label, or sign at the distance you entered before committing to the layout.

Selecting a preset restores its starting values. If you want to keep a comparison, record the result along with the distance and font ratio. A size written on its own can be hard to interpret later, especially if you tested both print and screen versions.

Starting values for screens and print

These values describe the preset inputs, so they change when you enter your own measurements. The sign starts with Signage text, while the other presets start with Body text. For a sign viewed from two meters, enter 200 cm and keep Signage text if the wording is a short direction or destination. For a poster people stop to read, estimate the distance they will actually stand from the poster.

How viewing distance turns into font size

Imagine two lines extending from the reader's eye to the top and bottom of a lowercase x. The angle between those lines is the visual angle. It is measured here in arcminutes, with 60 arcminutes in a degree. The diagram exaggerates the angle so you can see the relationship. The calculator adjusts the target angle for the text type, lighting, and visual acuity, then uses the viewing distance to calculate the physical height of the letter.

With Book, magazine at its defaults, the angle is 13 arcminutes. At 40 cm, that gives a lowercase x about 1.5 mm tall. Dividing that height by the font's ratio of 0.47 gives a font size of about 9.1 points. Double the distance to 80 cm and the calculated size doubles to about 18.2 points, with the other inputs held fixed. This relationship makes the calculator useful when adapting an existing design to a different reading distance. See the geometry behind this approach in the Legibility.info calculation notes.

How to choose the text type and lighting

Use Body text for continuous reading, such as a paragraph in a booklet. Consultation text is for information a reader looks up briefly, such as an entry in a list. Display text covers prominent lettering, while Signage text is for short signs and directions. A poster can contain more than one type. Work out the size of its main information separately from its smaller supporting text.

Lighting changes the estimate. Try Sufficient / medium or Poor when the text will be read under weaker illumination. Lower visual acuity values also increase the calculated size. These inputs describe a design scenario. Check the result with intended readers if you can. Strong reflections, poor contrast, crowded spacing, and thin strokes can still make lettering difficult to read.

Measure x-height and use the right units

To estimate a font's ratio, set a lowercase x at a known size and measure its height in the same units. For example, a 2.5 mm x in type set to 5 mm gives a ratio of 0.50. On screen, an x-height of 10 pixels at a font size of 20 pixels gives the same ratio. Measure the actual glyph from baseline to top and leave out the space above or below the line. A capital X or a letter with a tall stem gives a different measurement.

For print, use the result in points and compare the lowercase letter height in millimeters on a proof printed at its intended scale. For screen presets, the virtual resolution expresses how many logical pixels fit in an inch under the chosen scaling. It can differ from the physical pixel density on a device specification sheet. If you can measure a displayed element of known pixel width, divide that width by its measured width in inches to estimate the effective density. For web layouts, the W3C explanation of CSS length units describes why a CSS pixel can differ from a physical screen pixel.

Check the result in a real layout

Try the Cursive Handwriting Font Generator to compare how letter shapes change at the same nominal size. Check the finished wording in context, especially for scripts with small lowercase bodies and large flourishes. For printed designs, the cursive wedding invitation guide explains how to proof names and event details on paper. If your text uses small capitals or raised Unicode characters, read the small text generator guide to see how those characters differ from changing the font size itself.

A minimum estimate works best as the first setting you test. Give paragraphs room to wrap, check line spacing, and try the least favorable reading position. A website also needs to remain usable when the reader enlarges the text. See the W3C guidance on resizing text. For projects with formal requirements, consult the published DIN 1450 standard and any requirements specific to your project.

Frequently Asked Questions