Thread: converting imperial to metric visa versa

I made a pair of bedside tables and well into the construction realized that there was a typo. In one place on the plans it said 11 inches not 11 1/2 inches. So my tops didn't fit the bases.

So it's a really good idea to check the plans before you start and that's a good time to convert and round. 12 inches becomes 300mm and so on. Making sure everything adds up and will fit together.

In 1981 I was thrown in the metric deep end and had to learn fast. It didn't take long and I am still convinced that metric is

as significant as the invention of the router for woodworkers. We do a lot of calculating and fractions aint natural. We had

to learn the decimal equivalents of the foot to use our calculators.I used to know them all but only remember the easy ones.

3in= .25__6in= .5__9in=.75__12in=1

The antique trade and surfboards, in Aust, seem to persist with imperial. Lutherie is vexing because a lot of plans and discussion comes from the U.S.

Here at 53N, I could try to do woodwork in metric but it isn't worth the pencil lead.
Our economic relationship with the United States precludes most of it.
1. Never try to work in feet & inches. Total inches only.
2. If it looks like it matters, multiply by 25.4, NOT 25, to get mm. Maybe that doesn't
seem so important but that's a difference of 4mm over 10 inches. With my crappy
furniture skills, I need all the help I can get.
= = =
The real downside is any sort of mechanical repair:
Well, what did I get? Imperial? Metric? I must have both sets of wrenches
as most of what I own is a barstid mix of both!

Originally Posted by A Duke

That's an oxymoron metric does not work in dozens.
Regards

That's the joke

Originally Posted by elanjacobs

That's the joke

Then the joke is on me.
Enjoy

Thanks to all that replied, i have used some of the nifty apps on websites available through google and on iphone, i wanted to guage how other woodworkers with more experience than me approached the situation I stick to working with metric but when i dont have a choice and the plans i have is imperial i wanted to know "do i convert them?" or just get more comfortable working with imperial.

I have a few ideas now to how i can approach my furture work so thanks again for the ideas guys!

oh and happy new year!!!

I whipped up a little calculator in Excel a couple months ago. I'm building a Gerrit Rietveld chair and the original plans are in metric. After I got to thinking though, I changed my tact and decided to follow the plans and use metric, so I picked up a tape measure with a metric scale. The nice thing is that it has both imperial and metric, so it's easy to convert any measurement just by looking at the tape.

Hi Ball Peen,
It might be a nice Idea to show us a S/Stick, Bill, & for the Younger Woodies to know how to use one.
Maybe a couple of Photos & an Explanation on their use.
I knew am Older Woodie that used one, but it was to much for my simple brain.

Pete,
The mixed tapes seem good at first but at best they are a nuisance. You can't read from both sides and you think in two systems. The hardest part for a newcomer to metric is having a mental grasp of different lengths. Start with your own height, an internal passage door is 2.1m x 820mm., sheets of board are 2.4m x 1.2m.

Originally Posted by Master Splinter

There is a fair bit of crossover between the systems, not to mention blurring of the lines and the imprecise nature of wood.

Many of the 'metric' measurements are a simple metrification of an existing imperial standard, and in some cases you'll find the metric size on something as nominal, and the actual size translates back to the imperial measurement. Other times, it'll be a strict conversion to metric and the imperial measurement is approximate.

The approximations that I find useful are:

3mm = 1/8 inch
6mm = 1/4 inch
9mm = 3/8 inch
12mm = 1/2 inch
16mm = 5/8 inch
18mm = 3/4 inch
25mm = 1 inch

You'll note that materials like MDF are commonly available in sheet thicknesses of 3, 6, 9, 12, 16, 18 and 25mm...so most of the conversion is already done for you!

some of those conversions would never work for me , e.g i use 10mm instead of 9mm for 3/8 , i'd never get a 3/8 piece of hardware or timber into a 9mm hole or slots, same sort of problem with some others , almost never get 1/2" into 12mm spaces either, i use 13mm, 16mm for 5/8 is ok, 18mm doesn't work for 3/4, 19mm works better, 25mm sometimes works sometimes doesnt for 1", but its close enough to use (or try)

i adjust plans (if i want to convert them), simply take the import measurements and adjust the rest to (metric) fit, pretty easy with metric, for furniture i often use storybook or as i call em marking rods, the plans (for furniture) i draw on matchboard with the important measurements (which also take into account the most of typical timber widths available (here) so minimise wastage, then put i them on a shelf like books, even the most complicated plans fit on a small piece of board about the size of a small book, so i guess they are my story books they take up more room than if i put them on paper but i can throw em around the bench or whatever and they dont get damaged or lost , i have plans like this that are decades old now (house plans i put on paper lol)



cheers
chippy

Originally Posted by issatree

Hi Ball Peen,
It might be a nice Idea to show us a S/Stick, Bill, & for the Younger Woodies to know how to use one.
Maybe a couple of Photos & an Explanation on their use.
I knew am Older Woodie that used one, but it was to much for my simple brain.

See new thread
https://www.woodworkforums.com/f187/s...2/#post1593409

Might as well chip in with my 2 cents worth....

i use both measurements.....comfortable with both....in fact at times find working in imperial easier.

If I use any plans I use the measurement system on the plans and don't convert.....couldn't be bothered with converting. In most cases the measurements are more of a guide.....you end up cutting to fit anyway!

cheers

Originally Posted by simops

Might as well chip in with my 2 cents worth....

i use both measurements.....comfortable with both....in fact at times find working in imperial easier.

If I use any plans I use the measurement system on the plans and don't convert.....couldn't be bothered with converting. In most cases the measurements are more of a guide.....you end up cutting to fit anyway!

cheers

Good to know, i think this is the most common sense/practical approach i should take. Just measure and work in inches. The more i use it the better i will get so its just practice.

Thanks for letting me know how other woodworkers work

Work in one system or the other, the day of the week doesn't matter.
My only caution is that when you try to make conversions, stuff gets rounded off.
That is a recipe for disaster.

OK, suppose I have to make a drawer (draw?) front.
Plan says 15 inches. I'm determined to work in metric,
so I multiply 15 by 25mm and cut the wood.
That drawer front is 6mm too short. Dang near 1/4 inch too short.
You have just up-screwed big time. Duh, 1" - 25.4mm.

Just don't. One, or the other, or both side by side.
Apples are not oranges.