Circular pad properties scaling 1/2 the grid settings

Kicad 5.1.8 running on Windows 7 SP1 64 bit
Footprint editor, distances set in mm, User grid set to 0.0100mm.
I placed a circular pad, properties 0.450mm width/height, drill 0.260mm at position (0,0).
When I use the caliper tool, drill size measures 0.13mm and pad radius 0.22mm, exactly half the dimensions I configured! The measure distance bar at the bottom of the screen displays the exact measurement as the caliper tool.
If I double pad properties and set drill=0.520mm and pad width/height=0.900mm the caliper tool gives correct results.
What is happening? Is there a scaling setting that I am missing?
Thanks for the explanation!

Welcome to the forum!

After using a drawing CAD program, I went to use KiCad and found I had done something similar. KiCad’s footprint editor does not mention if it is using diameter or radius to determine the pad/hole sizes.

Thanks, Sprig, that is a great tip.
I´d better trust the caliper measurements and the XY position bar!

I think there are several reasons to use diameter instead of radius.

  • Rectangle pads use the whole length, not half of it.
  • With through hole component leads we always talk about diameter, hence
  • Hole size is defined as diameter.
  • Hole size uses diameter also because drill bits have diameter in their specifications.
  • Component data sheets have usually diameter, not radius.

I haven’t really used other EDA software but I think diameter is used universally and is just assumed.



I checked the interwebs and it is; but even before that I was fairly certain that it is standard practice to describe hole sizes with diameter and arcs with radius. I didn’t like the way the tone of my post was likely to come across to a new poster.

And besides, I really did have a brain fart and started drawing in KiCad and got the dimensioning bassackwards. I stared at the drawing on the screen for several minutes wondering why it just did not look right.

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Hi ehofmann,
You need to set the grid as per the minimum requirement of the hole size. Try to maintain the grid setting in the multiples of hole size, and it should be less than that.
The minimum grid setting should match the hole size. It should be lesser than the hole size and not more than that. If the center of the grid doesn’t match with the hole, that will create a problem. There is no scaling factor. I think you are confused between the radius and the diameter of the hole. Check from where you are measuring.

Thanks, Amit_Bahl. Kicad is not explicit about hole parameters. As others pointed out, it is really simpler thinking about diameters, because it is directly related to drill sizes. This design required designing a custom footprint for an HDMI receptacle with no data sheet, I used a 1/100 mm caliper to take measurements. Setting the PC Board grid was challenging because most parts were measured in mils, and conversions are never exact.

Conversions are not exact, true. But the error with the caliper I bet is bigger than the conversion. The internal resolution of pcbnew is 1/10000 mm.

There is no need to match the grid and the center of the pad: the coordinates of the pad/hole can be entered directly in the pad properties.

It is recommended to set the anchor of the footprint at one of the holes or at the center of the footprint. I prefer the center of the footprint because is easier for rotations. But historically the anchor of a THT footprint has been set to pin1.

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