mm vs inches

[Stan Calow]

It was an old thread, but still seems to be alive. I too was taught in both systems in high school and college. I think it's pointless to focus on conversion formulas or rules of thumb. It's what you get used to seeing. Probably most people have a good feel by now of how big one or two liter bottle of soda is, for example. You dont have to convert it. Being anti-metric on principle is futile. Much of what we think is in inches and feet, like plywood and car parts, are already metric, we just dont know it. It's a world market and like it or not, the US doesn't set the world's standard any more.

[Michael Burnside]

Old thread, but not as old as this discussion. I find the arguments either way entertaining. Metric or imperial, I often use a calculator to confirm my measurements just as I do in my real job. I'd hate to tell my boss we need to repsin this project for 300k because "I did the math in my head". I know wood isn't millions of dollars, but checking with calc pro takes seconds and could save you a lot of time if you mess up. I've been known to screw up base 10 math just as easy in my head

And whatever you do, you should not convert back and forth, that's just asking for problems and is a stupid argument for either side.

I don't know about ya'll though, once I get my base measurements in, it's all unitless relative measurements anyway.

[Maurice Mcmurry]

On any digital device I always use Metric. On every analogue device I always use fractional inches. Finding a center is another time that I use mm

[Jim Becker]

Measurement systems are measurement systems. They all have value to the user. The only good universal rule is "don't mix them in a project".

I'm 100% metric in the shop unless i'm doing something for a friend who's specifications are in inches and 95% inches/feet for construction. After five years, I'm no longer mentally visualizing the conversion anymore, other than in long lengths.

[Derek Cohen]

I am conversant with both systems, having grown up with Imperial until I was 10 or 11 years, and then Metric was adopted.

For much of my woodworking life I was pretty solidly Imperial, simply because all the old hand tools (chisels, plough plane blades, drill bits, etc) were Imperial. However, when I acquired a Hammer A3-31, it was Metric, and that changed everything. Somehow the thickness of boards became the foundation for all that followed.

Very gradually, router and drill bits are moving to Metric. The irony is that Metric router bits require a 1/4"- or 1/2" shaft.

Regards from Perth

Derek

[Brian Holcombe]

I prefer to measure in decimal inches over anything. My equipment is european so aside from router bits, everything is in metric.

Alternatively, you can just make everything a multiple of 8mm (5/16") and you'll be working metric and imperial at all times.

[Bill Howatt]

...
Very gradually, router and drill bits are moving to Metric. The irony is that Metric router bits require a 1/4"- or 1/2" shaft.
...
Derek

And my metric sockets use a 1/4, 3/8 or 1/2" drive ratchet.

[mike stenson]

And my metric sockets use a 1/4, 3/8 or 1/2" drive ratchet.

Gotta love legacy standards.

I have a die grinder with a metric collet, it sucks because finding metric bits is a pain.

[Jim Dwight]

I have no problem at all with people who prefer metric. It is a good system - for them. But I do have a problem with them or anybody else saying metric is a "better" system. It is not for me. I grew up with feet, inches, and fractions. I cannot envision how big something 27cm is unless I convert it to inches. I cannot envision how much 3 kg is unless I convert it to 6.6 pounds. But for those who know what 27cm is and what 3kg is, go for it.

The best way to measure, however, is not to do it. If it wasn't so cold in my unheated shop I would be there right now cutting down a couple 2x4s to fit the rails on a bed I am making (I use cheap 2x4s to support the slats which support the mattress because they are cheap, sturdy enough, and won't be seen). They need to be the same length as the bed rails and I have a stop already set for that. So the same stop will be used. Any time you can measure off a part you want to mate up to you should. Much less chance of error that way. Story sticks are another way to help minimize errors. You have to do the measurements once in many cases to make the stick but then you can reuse it for all the dimensions in the project that length. Regardless of how you measure - which system you use - measuring is an opportunity to make a mistake.

Trying to force others to use the system YOU prefer is just silly and immature. It pushes them in the direction of mistakes. I can use metric, I have to to use my domino which I love for making mortises, but I prefer to use the system I can visualize better. I don't think it's inherently better or worse than metric, it is just what is easiest for me to use.

[Justin Rapp]

A lot of my tools are Inches (table saw scale, router bits, chisels, etc.). For that reason alone, I mostly use inches.

--Whit

Same with me. Most tools in the US are in inches, and I got used to doing fractions really well, and even converting from / to fractions and decimals for most of the common sizes but I still need to do a little math when I find something that says 7.28125 inches. Or 7 9/32. I did find this cool chart that has fraction, decimals and MM for every 64th between 1/64 and 1 inch. They sell them on amazon but I found a PDF online and just printed it.

[Lee Schierer]

I use my metric adjustable wrenches all the time.

[Michael Burnside]

I just laugh when people talk about how fractions are hard as if that's the argument. If they're hard for you, it's just stick to 16 equal divisions along 1 inch. Instead of 1/2" just use 8/16", instead of 5/8" use 10/16". If you want half of 5/8 it's pretty easy to get half of 10/16, it's just 5 instead of 10, so 5/16ths. Honestly if that's all it is, you're over thinking it. The metric folks that try to pull out a 1/32 or 1/64 just lose credibility, not that it's hard to add 1/32 to 10/16th, which is just half way to 11/16ths, but somehow 16.5mm is easier LOL.

I used metric for a couple of years, but between some tools I really liked being in inches and just not seeing any real value with either system, I just went back to imperial when I decided to refresh the "beginner" tools with "pro" versions and I gave the rest away and replaced with imperial. If there is any argument to be had, honestly I find it easier to see the 1/8 and 1/4 graduations on rules with my eyes, but otherwise, neither has any benefit in woodworking. Elsewhere, I think the argument can be made for metric, just not woodworking.

[Mark Hennebury]

I don't measure anything that I don't have to. I use a knife, a square and a story stick. I have no idea what the actual measurement is. If i have to make a countertop, I template the wall. If I have to fit a built in cabinet I use a story stick and transfer measurements, I use plumb lines and levels, have no idea what the measurement is but I know the cabinet fits the space, and that it is plumb and level. Worked on sailboats interiors, everything is referenced of a centerline. If I am cutting stock same thing, everything is referenced off the stock and transferred, no measurements required. Mortises are cut based on the mortise chisel width, the tenon is made to fit the mortise. I don't care if the mortise is 0.250, 0.255, 0.245 etc, it is what it is, I make the tenon to fit.
You don't really need to measure much at all. Who cares if a table top is 40" +or- 1/16" as long as your joints are tight and all parts are that are supposed to be the same size, are the same size.

[Curt Harms]

There is one other issue I don't believe anyone has mentioned -- hardware. Walk into any U.S. hardware store or home center and peruse the selection and price on imperial hardware compared to metric. Yes they have metric nuts and bolts but smaller selection and bigger price tag. I've never done this in a metric country, it would be interesting to do so.

[Patrick Johnson]

As a designer in the auto industry, I've always designed in metric. In my shop I primarily design and work in inches, sometimes fractions, sometimes in decimal inches.

I think both measurement systems are like a language that you have to learn and become fluent in. If you can do that, it doesn't really matter which system you use.

Patrick