Imperial or SI?

Measurements is meaningless unless you know the uncertainty, Walter said. Being a physics professor, SI units was the norm. Join the dark side of the empire, and you’ll wonder how many Fahrenheit there are in a cup.

Walter Levin is famous for his lecture style and energy. I’ve enjoyed the videos from his lectures at MIT tremendously! I once studied for a degree in computer engineering, and really enjoyed the physics course. So much so that I got a B. I did not get my degree – life got in the way – but I have my knowledge in the physics realm. I therefore understood perfectly what Walter meant. There were units of measurement that I found hard to really understand, though. For the most part in the more esoteric corners of the university physics syllabus. The fact that university physics is metric made things easier on me of course. I am Norwegian, and Norway adopted the metric system in 1875 – only two days after the metric convention was concluded. The metric system has been with me all my life, and has been the official system since 1875. Yet – some dinosaurs in the unit family doesn’t seem to go extinct just yet.

This is a "rant" - an article where I give my opinions on things. Usually, the rants are triggered by something I read or see online. In the rants, I do not try too hard to be unbiased although I try to be accurate and do think things through. I lean on other opinions as well, from well established folks that has proven themselves. At the front of that line, you'll find Paul Sellers and Richard Maguire (the English woodworker). Read this article as it is intended - informative, provokative and with a large amount of humor. Then draw your own conclusions.

Despite the fact that Norway is metric, eggs still comes in packs of 6 or 12 here. When buying wood (construction materials), I ask for two-by-four’s and get 48x96mm materials; they know what I mean. I am used to think of 2×4-6-8” in construction, and I “know” how big those sizes are. At the same time, I have NO idea how many inches – or fraction of an inch – a 19mm thick siding panel equals to, but I have a pretty good idea on how thick that is

Square eggs – metric or not? Shipping containers are imperial, so…

In the beginning of my “woodworker career”, I bought some white oak and some ramin for my organ project. That was the first time I had a run-in with board feet. Did not compute at all – even the people working at the outlet had troubles, and had to ask that one special guy about how much I had to pay. You know, the one person that knows everything – lo and behold if that person is sick or not available; everything grinds to a halt.

Over the recent years, thankfully, we’ve seen that lumber pricing here has moved from board feet to litres. In a SI world, this is good news. If you add up the measurements in decimetres, you get litres. Deci means tenths: one decimetre is 1/10 meter, or 10 centimetres. one cubic decimetre equals one liter. A board foot is 2.35973722 liters…. No need for the special someone at the lumber place anymore…

Moving from system to system

It does become interesting, though, when the society adopt metric in areas that formerly were the domain for imperial measurements (or any other system of measurement). I know roughly how big a 22 foot boat is, but a 6.7 metres long boat does not mean much to me. When dreaming about my future French yoghurt container (Jeanneau Merry fisher or Benetau Antares are at the top of the list), I have to check the specifications sometimes – is that really a 21 or 22 footer? By writing this, I actually start feeling a bit old. I can remember coming with my mother to the butcher shop when I was a kid, wondering about how much cold cuts she bought when she asked for “two hecto”. It is 200 grammes, in case you wonder.
Times gone by… But my future flag ship fishing boat WILL be 21 or 22 foot. No matter what the stickers on the sides says!

What’s that you said??? Not the unit you’re looking for?

Other evidence that metric still has a way to go is evident when I want to chuck some hot dogs on the fire pan. They come in packs of 6 or 10. The buns in packs of 8 or 12. However, it seems that the bun business is catching on. Now the packages usually contains 10 buns – usually, this indicates that somebody in that company has actually extracted their heads from their arses and concluded that they came in second on the old conundrum of the hen and the egg. “It’s how we’ve always done it” is a phrase that usualy give me more nervous ticks than a Lyme disease research facility, and I regard it as an indicator on stubbornness for the sake of being stubborn. If the sausages comes in tens, so should the buns. It’s easy, really. It’s the metric for success!

We just need to tell the hens. Those eggs comes in 6 or 12. Half or full dozen.

Simply the best!

I’ve read quite a lot of discussions, arguments and debates about the topic metric vs. imperial. Do a quick google, and “imperial vs metric woodworking” yields almost five million hits. Five. Million. Hits. I suspect that the vast majority of the forum thread debates included in those 4.900.000+ hits quickly turns into the old game of “Which is best?”. A.k.a. pissing contest.

That question is STUPID!

Source: Deviant Art

Which is best, one inch or 25.4 millimetres? The distance is exactly the same. It is sort of like arguing about which end is shortest of a piece of rope. There is one simple conclusion to this topic: The best measurement system is the one you are most familiar with! Use that one.*


Arguing about which numbers on the ruler is best is STUPID! Go make shavings in stead. Or rake snow, as long as you do something in stead of wasting electrons. Yes. I am being crass. It’s to get the point across that quarreling about certain things are a waste of air.

*Unless you make furniture for the NASA offices, in which case you should clarify which system they expect you to use… Goodbye, MCO. may you rest in pieces!

The imperial units are not inferior in any way, but I’ll say this about the metric system: it is FAR easier than the imperial system when conversions needs to be made. You multiply or divide by 10. Or move the comma to the right or left.
1000 millimetres = 100,0 centimetres = 10,00 decimetres = 1,000 meter = 0,1000 kilometer = 0,01000 scandinavian miles (yes, we do have our own mile, which is 10 kilometres or 1000 metres).

As for conversion within the imperial system, Innes McKendrick has once and for all elaborated on the subject in a famous twitter thread, in a way far, far better than I could ever hope to come up with. Read about it here. It is hilarious!

Simply the best. Better than all the rest. Tina answered that question for us once and for all! The one YOU love!

The relative solution?

In any rate, I think we should not spend time arguing about which system is better. If you are used to the imperial system, use it. What system of measurement we use, really does not matter for what we do. Relative dimensioning solves all those problems for us. Marc Spagnuolo talks about this in his article and video. Basically, you fit one thing to another. Whether the thing is 284mm or 4544 mickeys (16 mpi) is irrelevant as long as Piece B fits between A and C.

Measuring tape and folding ruler compared. Note the difference??? Source:

In the image above, another problem is shown – can you trust your measuring device to be accurate? This is why you need to stick(!) to the same device when measuring – if not, you need to verify that your different measuring thingamabobs agrees on how long an inch or a millimeter is… This diagram from an article at the Norwegian organization Forbrukerr├ądet shows significant deviations on a lot of high-end measure tapes. Some of the cheapo’s were among the best ones, actually. Expensive is not necessarily best…

Say you want to build a chest of drawers for your bedroom. If you have an alcove where the piece will stand, you have some constraints to account for. If it will be placed somewhere along a wall, you have more freedom. Perhaps then the size of the drawers become the crucial part. If the outer dimensions matter most, you might opt top design the piece to fit within those dimensions – and make the drawers to fit the carcass. If not, build the carcass around the drawers as it might behoove you to consider their size first and foremost.

On the bench, you do not need to care about exactly how long a table’s legs are. Make the first leg (or a leg template), then make the other legs to match the first one. When cutting a dado for a shelf, use the shelf itself to mark for the width of the dado. You mark the the initial line, for example based on a given distance between two shelves, make a knifewall then place the shelf into the groove for the knife wall. Then mark the second line using the shelf as a guide. It does not matter if the shelf is 14 or 14.6mm thick. It will be a SNUG fit either way. The story stick will be much more efficient than any ruler, and it will be dead on every time.

The butler stick. The story stick works in a similar way.

This is an elaborate way for me to point out that you should not be too concerned about measurements. The wood machinist movement has enabled us to be extremely accurate, so it is only natural that we do focus on exactness and measuring. Move away from the constraints of the machine, and you really do not need a measuring device all that much. Using a dado stack in the table saw for a given size of wood, and you need to be concerned about the numbers. Use hand tools for the same operation, and the numbers are irrelevant. Whether they are metric, imperial or imaginary!

For the time being, we’ll have accept that the systems will co-exist. Even though the imperial system is officially used only by about 5% of the world population, it is obvious to me that the imperial system is still kickin’ among us SI-dominated people. The example on the boat length proves to me that we should not argue about which system is best. I know very well that a 8′ dinghy makes for an interesting ride in choppy swells, but a 250cm long boat sounds okay-ish to me. It is the same length… I somehow understand roughly how much power my 2 HP band saw has, but the fact that it delivers 1.5 kW on the shaft means nothing to me. Maybe except that it sounds warm. 1500W is a big stove hotplate…

To me, the only interesting part of the “metric vs. imperial” quarrel – is the fact that people actually argues about such nonsense. The rope does not care how long its left end is, and neither should we. My only issues with the different systems (not limited to measurements) are the likes of: we still need to make cars with the steering wheel on the right side. I own an imperial socket set from when I owned a Massey Ferguson 135 tractor because that model was built with imperial measurements, but I haven’t needed the set since.
At 22┬░K I’d be dead, at 22┬░F I’d be pretty cold and at 22┬░C I’m rather comfy. Funny thing is that the C and K are both metric. Better be careful when setting the thermostat, I reckon…

I try to please both camps, so you’ll find that I give measurements in both metric and imperial in my articles – for the most part. Just remember the relative dimensioning thing – take your measurements directly from the wood. You might find that you do not need to concern yourself with a single digit of measurements. Freedom.

It seems that the world inches towards the full implementation of the SI system. One brand of hot dog buns at a time…

Leave a Reply

Your email address will not be published. Required fields are marked *