What is connector pitch and how to measure it?

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Pitch is defined as the center-to-center measurement between two pins/legs of the component.

Connectors in particular are always categorized by manufacturers/retailers based on pitch, so it is the single-most important property to learn about when trying to identify or specify a connector.

A photo of a connector with no measurement or scale is therefore not very helpful, since without knowing the pitch, we'll be fumbling around in the dark.

Historically, pitch was often stated in inches with the classic header/socket strips measuring 0.1" (2.54mm), which was also the standard pitch for IC using through-hole DIP packages, whereas SO SMD packages often use a 0.05" (1.27mm) pitch. Nowadays the SI ("metric") system is normally what is used and what you are guaranteed to find in datasheets and drawings, whereas measurements in inches aren't always available. So it is best to stick to millimeter.

Because of this, common pitches tend to come in two flavors: those based on inches and those based on millimeter. Common standards for pitches are 1.27mm, 2.54mm, 5.08mm because they were based on multiples using the inch system. And other common standards based on millimeters are 0.5mm, 1.0mm, 2.0mm, 5.0mm.

This causes a bit of head ache - 5.08mm vs 5mm is particularly difficult to tell apart (if they are connectors they may even mate, though a bit poorly) and there are oddball pitches like 1.25mm which is easily mixed up with 1.27mm.

To measure a component's pitch, the easiest way is to use calipers and measure the total center-to-center distance between the outermost legs. The longer the distance measured, the smaller the measurement error. Then divide the total by the number of "between pins" sections - that is, the number of pins minus 1.

Example: See the picture below. If I have SOIC16 with 8 pins per side, I could measure the distance between pin 1 and 8. Measuring from pin 1's left side to pin 8's left side, which is equivalent to the center-to-center distance. I get roughly 8.9mm. Then I divide this by 8-1 which is the number of pins minus 1.

8.9 / (8-1) = 1.2714 so the pitch is 1.27mm (0.05"). The 0.0014 was a caliper measurement error.

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