Metric Inch Conversion

From the CAD Library: Inch-to-Metric Conversion Tables

First, let me start out with a few tips about metric speak that all PCB designers need to know. Metric is not a unit of measure. Metric is a term that describes a measurement system. You use either millimeters or microns for your PCB design units. The proper terminology to describe your working units when using the metric measurement system is millimeters or microns, not metric. For example: When doing PCB layout in inches or mils, you never refer to working in "imperial units.” The same holds true with metric.

Millimeters allow finer (and greater) granularity in the PCB design grid system to optimize board real-estate, part placement, via fanout and routing trace/space features and snap grids. This will be very important in the future of PCB RF microtechnology. PCB impedance measurements are more accurate in micron units than “ounces of copper” and mil core/prepreg dielectric. Use micron units to achieve the highest level of accuracy for impedance calculations.

Why Hasn’t Metric Caught On?

Unfortunately, PCB manufacturers are directly responsible for holding back the progress in the transition to metrication of our industry. When the PCB fabrication companies transition to the metric system, the entire electronics industry will achieve the peak of electronic product development automation. Until then, we’ll plod along using dual units in the land of chaos.

Here is an example of the chaos in the chip component family. All chip names refer to their body length and width. When EIAJ introduced the standard chip and molded body component dimensions, only millimeter units were used. A 3216 was 3.2 mm long and 1.6 mm wide. It was all very simple. When the data was passed on to EIA in America, they changed all the chip names from millimeters to Inches and a 3216 was renamed 1206 or 0.125” length and 0.062” width (just drop the third-place number). Today most component manufacturers dimension all of their component packages in millimeters (see Table 1 for illustration of metric vs. imperial names.) You can easily see the confusion in the dual measurement system.

Metric Conversion From US Stitches Per Inch | The Temecula Valley ...

All of the sewing machines that I have seen that were made in the last 10 or 15 years have stitch length settings that are in millimeters. Back when sewing machines were still being made in the US, most of our sewing machines had stitch length settings that were in stitches per inch. The picture to the right shows the stitch length knob of an old Singer sewing machine model 750.

Most of the world uses the metric system, and it probably won’t be long before the US does too. For now, if you don’t want to learn the metric system, you can simply do a little math to convert the number of stitches per inch that you desire to the metric equivalent used by your sewing machine.

While browsing the Janome Forum this morning, I saw that a forum member had asked how to convert the metric stitches to stitches per inch. It’s a really easy conversion to do, and you can do it with a calculator.

In English that equation reads, “25.4 divided by X equals Y”. X is the number of stitches per inch you want, and Y is the setting in millimeters for your sewing machine. You will probably have to round your answer to the nearest tenth of a millimeter, because sewing machines don’t have higher accuracy than that. In some cases, your sewing machine may only increment it’s stitch length setting in half millimeters, so you would round up or down as needed.

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