# With all these new power tools, why do we still measure in the dark ages?

 Blog entry by technicallymark posted 04-08-2010 08:27 AM 2155 reads 0 times favorited 51 comments

Quick, which is bigger, 5/16th or 11/32nd? Having trouble? Try this. Which one is bigger 10 or 12? Easy right? I’m all about easy and trying to remember how to convert fractions isn’t really something I want my brain working on with spinning sharp blades around.

I’m not sure why we can’t be like the rest of the world and use “metric” for measuring, but it would make life a little easier in the shop. I might be a little biased since I have formal education in biological science, but the company I work for makes machinery where all measurements are based in metric. Since I’ve really just begun on my woodworking journey, I have not yet invested in a good metric tape measure, but I do have a 300 millimeter ruler with a great straight edge that is handy and reliable.

On that same ruler, if I’m measuring from zero to say 10 and 5/16th inches, the ruler just isn’t marked for that kind of accuracy. Yeah, I know most people probably only measure to an 1/8th, but if you make smaller projects, smaller increments just might come in handy. So if you’re shaking your head yelling at me about how difficult the metric system is and its just a waste of time, I have a few tips that might just get you started thinking metrically, which will eliminate all those annoying fractional conversions swimming in your head.

Rule 1: One inch is 25.4 millimeters or 2.54 centimeters. Measuring in millimeters is actually more convenient when talking about a 4” board which is really just 102.0 mm. Your blade if you have an average table saw is 254.0 mm(10 inches).

Rule 2: Converting from fractions can be done but its not very fun. Take 11/16ths. If we do the math on that fraction we get 0.6875 inches(I love decimals). Now you simply multiply 25.4 mm(again it equals one inch) with the number your calculator gave you when you punched in the fraction. So the big conversion is 11/16ths is equal to 17.4625mm. Unless you use a pocket microscope, you probably won’t be able to tell the difference between 17.4625 and 17.4999, and it really doesn’t matter. I’ve found my eye can differentiate at most a 0.1 to 0.3 mm difference in measuring an object on paper.

Maybe I’m just angry towards my grade school teachers who told us all of the US would be metric by the time I graduated from high school. The only metric that has seemed to stick since 1985 is a 2L(liter) of soda in a bottle. I think wine and liquor are measured in milliliters but I don’t drink much other than beer.

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My next project is a mobile base for my contractor’s saw with some storage in it. Here are the standard SAE dimensions that I want it to be. 24 inches wide, 32 inches long, and 21 inches high. But I think I’ll work on bringing my work brain into the shop. I’ll make it 610mm wide, 813 mm long, and 533 mm high. And I’ll add 51mm high casters with locks on two of them.

The ply from the lumber yard is 23/32nd, or almost 3/4 inches. But really, its 18.3 mm(rounded up) thick. I’ve seen other ply marked as 12mm without any fractional dimensions. What could that be in inches? Well, 12 is almost half of 25.4, which we know is one inch, so indeed, it was 1/2 inch ply.

Look at the rulers below and tell me which one is easier to read? I quickly did a search and found Lufkin makes a nice looking tape measure with the primary marking metric, which is probably what most of us use when we measure something left to right. Let me know if you hate or love the metric system or even if you are considering warming up to the idea.

-- Love the taste of sawdust in the morning!