Thread: Metric / Imperial relationship reference

I began Imperial and converted to metric so I can use either system happily, though I do prefer metric. Your chart will be a quick ready-reference for many people. Thanks for posting it.

David

Thanks for your chart,I started my apprenticeship in the printing industry in the late 50's and all the machines were German so everything was metric,at trade school paper sizes and weight was all GSM,grams per square metre
so metric was easy for me before it became law,what an easy way to measure things so much more accurate than 11 and 1/3 or 11 15/16th
Why did me take so long to change to metric

Under an inch isn't that hard, all you have to remember is that 1/64" is close enough to .4mm. By the time you get to 1" you're only .2mm out, generally good enough for woodwork.

Stick to metric it's a lot easier for old farts like me

I understand what you are trying to do but mathematically speaking the relationship is not really as you have shown it.

Inches = millimetres / 25.4
OR
mm = Inches X 25.4

Hence a mathematical relationship between "mm" and "inches" is a graph with a dead straight line with a slope of 25.4.

Your graph uses varying increments 1/32" 1/16" etc on the Y axis so it not really a true X-Y variable graph but as you say a "Chart" which is really just another term for a "Table".

Converting between decimal mm and inches is easy, just multiply or divide by 25.4
Converting between fractional inches and mm is not that much more of a deal but a table can be very handy and there are plenty of them out there on the web.
Look for "drill size charts"

I have some of these drill size charts pinned up in my shed but now I find myself using my Digital calliper with the fractional inch display as it does the conversions between mm/inches and factional inches with the press of button to 1/64 of an inch.

@aldav and @nrb, I can assure you that I'm sticking with metric! I have no intention of trying to work in imperial. As I said in my OP, my problem is watching YouTube videos where they talk about leaving a 16th gap etc, and have no internal reference to visualise what they're talking about

@BobL, mathematically speaking, the relationship is exactly as I've shown it. It's a visual representation of where the common imperial units fit along the scale of mms. Amazingly you'll find that they correspond perfectly with divisions calculated at 25.4mm per inch

Interesting that you mention there being plenty of charts on the web. My searches didn't turn up anything that "I" found intuitive. 10 minutes in Excel however, and I'm happy.

I'm glad you don't need it, because I certainly do!


Sent from my iPad using Tapatalk

I've usually got my iPad or phone with me so I keep this link in my Favourites:

FRACTION TO DECIMAL AND MM TABLE

It's a chart of length in fractions, decimal and metric from a ham radio enthusiast's site. Handy if I need it.

Brian

Xfigio, nice job thanks

Originally Posted by Xfigio

@BobL, mathematically speaking, the relationship is exactly as I've shown it. It's a visual representation of where the common imperial units fit along the scale of mms. Amazingly you'll find that they correspond perfectly with divisions calculated at 25.4mm per inch

I realise this is not a maths forum and am sorry to split hairs but its neither amazing nor mathematically correct.
I think you misunderstand what is meant by a mathematical relationship.
The only label I can give it is a visual representation of selected values which is the same as a table of values.

Your graphic gives the strong impression that inches to mm is a "curved" line relationship which it is not.
The Y axis shows mixed inches and mm, and the X axis show mm - at no stage does it show how one relates directly to the other.

The mathematically correct way to graphically express the mm to inch relationship is like this.
Screen Shot 2017-09-18 at 6.07.55 pm.png


One axis should show only one variable and the other axis the other variable - the resulting curve/line then shows the mathematical relationship.

The mm/inch relationship MUST be a straight line otherwise doubling the mm would not exactly double the inches and would be something more or less than exactly double.

I grew up a while ago so was schooled in both systems. I do visualize in imperial as I learned that first so find that is the natural way to woodwork for me. That said if I use sheet goods that are metric or if any tooling is metric like router bits then that whole project is metric. Never mix the two so no need to fret about relationships.
Regards
John

Nice work Xfigio.
I've always found that if it works for you and using it gives you the right results, it's a "go'er". I find it very easy to use.

Imperial and metric are both completely different systems, both are very easy.
Why try to confuse things by blending the two, just use one or the other.

Regards
Keith

Originally Posted by pedro66

Imperial and metric are both completely different systems, both are very easy.
Why try to confuse things by blending the two, just use one or the other.

Regards
Keith

Because sometimes you're working with imperial plans or imperial router bit sizes but every tape and machine you have is metric so you don't have much choice about it.

Originally Posted by elanjacobs

Because sometimes you're working with imperial plans or imperial router bit sizes but every tape and machine you have is metric so you don't have much choice about it.

That's a fair point, I don't personally have that problem as I don't work from purchased plans.
I do have both imperial and metric router bits and both in rules and tapes, so if I were to work from a plan it would not matter.

Regards
Keith