Points and picas are fixed
In digital publishing the point is defined as exactly one seventy-second of an inch and the pica as exactly twelve points. Historic printer's points differed very slightly, but no current software uses them.
Page layout software talks in picas, printers talk in millimetres and your cover designer talks in pixels, which is what this Typography Unit Converter is here to settle. Enter a measurement in whichever unit you have and read it back in all six at once.
Type a value, pick its unit, and the full conversion table rebuilds underneath as you type.
Typography inherited its measuring system from metal type, and the arithmetic has survived every technology since. A point is one seventy-second of an inch, twelve of them make a pica, and six picas make an inch. Those numbers look arbitrary until you spend an afternoon in a layout program, at which point they become the most convenient thing in the building.
The awkwardness comes from the boundaries. Type size and leading are specified in points, page geometry in inches or millimetres depending on where the printer is, and anything touching artwork in pixels, which are not a physical unit at all until you fix a resolution. A pixel is only a real measurement once you say how many of them fill an inch.
Most production errors are conversion errors. A cover exported at ninety-six pixels per inch instead of three hundred, a bleed specified as three millimetres where the printer expected an eighth of an inch, a text block set forty picas wide when the trim only allows thirty. None of these is hard to avoid once the numbers are in front of you.
In digital publishing the point is defined as exactly one seventy-second of an inch and the pica as exactly twelve points. Historic printer's points differed very slightly, but no current software uses them.
A pixel has no size on its own. It only becomes a physical measurement once paired with a DPI figure, which is why print artwork is prepared at three hundred while screen graphics sit at seventy-two or ninety-six.
European and Asian printers usually specify in millimetres, so a three-millimetre bleed is common where an American printer asks for an eighth of an inch. They are close but not identical, and rounding between them causes trouble.
Line length is traditionally specified in picas because it maps cleanly onto type size in points. A comfortable measure runs roughly sixty-six characters, which for most book faces lands between twenty-four and thirty picas.
Forward your printer's requirements to us and we will translate them into a working layout specification, then build the interior to match it exactly.
The exact relationships this converter uses, expressed against one inch.
| Unit | Symbol | Per inch | Equal to | Used for |
|---|---|---|---|---|
| Inch | in | 1 | 25.4 mm / 72 pt / 6 pc | Trim sizes, margins, bleed in the US |
| Millimetre | mm | 25.4 | 0.03937 in / 2.8346 pt | Trim and bleed outside North America |
| Centimetre | cm | 2.54 | 0.3937 in / 28.346 pt | Cover artwork specs, packaging |
| Point | pt | 72 | 0.01389 in / 0.3528 mm | Type size, leading, rule weights |
| Pica | pc | 6 | 12 pt / 0.1667 in / 4.233 mm | Measure, column width, gutters |
| Pixel at 300 DPI | px | 300 | 0.00333 in / 0.24 pt | Print-resolution images and covers |
| Pixel at 96 DPI | px | 96 | 0.01042 in / 0.75 pt | Web and CSS reference resolution |
| Pixel at 72 DPI | px | 72 | 0.01389 in / 1 pt | Legacy screen work, one pixel per point |
Seventy-two, in every current design and layout application. That definition, sometimes called the PostScript or desktop publishing point, replaced several slightly different historical standards and is now effectively universal.
A pica is twelve points, or one sixth of an inch. Designers reach for it because line length and type size then share the same underlying scale, so a twelve-point line in a twenty-four pica measure is a clean relationship rather than an awkward decimal.
Divide the pixel figure by the resolution in dots per inch. Three thousand pixels at three hundred DPI is ten inches; the identical file described at seventy-two DPI would be just under forty-two inches. The pixels never change, only the stated resolution.
Close but not equal. An eighth of an inch is 3.175 millimetres, so the American standard is slightly more generous. Supply whichever figure your printer specifies rather than converting and rounding between them.
Three hundred dots per inch at final printed size is the accepted standard for photographs and raster covers. Line art and text scanned as images benefit from higher figures, while vector artwork is resolution independent and needs no DPI at all.
Almost always because the file was built at screen resolution. An image that fills a monitor beautifully may only be a hundred pixels per inch when scaled to a real cover, which prints noticeably soft. Rebuild at three hundred rather than upscaling.
Use whatever your printer specifies so nothing is lost in translation, then let your layout software convert internally. What matters is that the exported PDF carries the correct physical dimensions, not which unit you typed.
Strictly, dots per inch describes a printing device and pixels per inch describes an image, but the two terms are used interchangeably in everyday practice. In both cases the figure simply states how many samples occupy one inch of physical space.
Measure, leading, margins, gutters and rule weights all specified properly and applied consistently across every page, so the finished book holds a single coherent grid from the half title to the colophon.
See Typography Formatting