# More Questions about the Metric System - House Construction **URL:** \ **Category:** Factual Questions\ **Created:** [July 18, 2018, 1:57am UTC](https://boards.straightdope.com/t/more-questions-about-the-metric-system-house-construction/818116 "2018-07-18T01:57:48Z")\ **Posts on this page:** 6\ **Page:** 3
**Author:** ![sbunny8](https://avatars.discourse-cdn.com/v4/letter/s/c77e96/32.png) [@sbunny8](https://boards.straightdope.com/u/sbunny8)\ **Post date:** [July 20, 2018, 1:32pm UTC](https://boards.straightdope.com/t/more-questions-about-the-metric-system-house-construction/818116/41 "2018-07-20T13:32:22Z")
There are several examples in construction where dimensions are given as approximate measurements in both SAE and metric. Take, for example, the specifications for drilling a hole through a door to accept a door knob. The backset (the distance from the edge of the door to the center of the cross bore) is typically 2 3/8 inches in SAE or 60 mm in metric.\* When you buy a door knob, the instruction sheet included in the box usually shows a diagram where this dimension is labelled both ways. Technically, 2 3/8 in = 60.325 mm, not 60.000, but the difference is small enough as to be negligible in this situation. Likewise, the diameter of the edge bore is labelled both as 1 inch and also 25 mm, even though 1 inch actually equals 25.4 mm. I have also seen tools that are labelled this way. A 1 inch spade bit (perfect for drilling a 1 inch diameter hole) will be labelled as 1 inch and 25 mm. I see that others have pointed out that a 2x4 is actually 1.5 x 3.5 but look at plywood. The “common” measurement of, say 3/4 inch, almost always corresponds to a slightly smaller thickness, usually 23/32 (which is 18.25625 mm). We could just as easily call it 19 mm plywood or even 20 mm plywood and keep manufacturing it at 18.3 mm and no one would notice or care. Of course, this doesn’t address the length and width, which I admit is another problem entirely. - That’s for residential applications. In commercial applications, the spec is 70 mm or 2 3/4 inches (which actually equals 69.85 mm). ---
**Author:** ![Nava](https://avatars.discourse-cdn.com/v4/letter/n/da6949/32.png) [@Nava](https://boards.straightdope.com/u/Nava)\ **Post date:** [July 20, 2018, 2:01pm UTC](https://boards.straightdope.com/t/more-questions-about-the-metric-system-house-construction/818116/42 "2018-07-20T14:01:56Z")
> [@md2000](#): > > Plus, the frame house (or frame inside brick) is more suited to places with a lot of timber and a need for good insulation. The first time I went for a walk in a small Swedish town, I had to fight a grin when I recognized the roots of so much of US architecture 🙂 But your ideas of “good insulation” and mine… differ. ---
**Author:** ![Hari\_Seldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hari_seldon/32/5173_2.png) [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)\ **Post date:** [July 20, 2018, 2:53pm UTC](https://boards.straightdope.com/t/more-questions-about-the-metric-system-house-construction/818116/43 "2018-07-20T14:53:07Z")
> [@Kiwi\_Fruit](#): > > NZ home construction is predominantly wood frame based so similar to the US. Construction timber is pretty much sold in all metric units, so 100 x 50 studs, but many people still refer to them as 4 x 2. Dry wall sheets are in 1200 x 2400 or 2700 sizes, as are plywood sheets. Stud spacing normally at 400 centres. Note that dimensions are given in millimetres and lumber lengths are in metres. But 1200 mm is about 3/4" short of 4’. So are they actually 1200 mm or really 4’? I have seen fruits and vegetables sold by the “pound” in Europe, but they always mean just a half kilo, which is more than 10% more. Here I have seen things priced by both the pound and kilo, but pound means 454 g. ---
**Author:** ![Chopsticks](https://avatars.discourse-cdn.com/v4/letter/c/cab0a1/32.png) [@Chopsticks](https://boards.straightdope.com/u/Chopsticks)\ **Post date:** [July 20, 2018, 3:30pm UTC](https://boards.straightdope.com/t/more-questions-about-the-metric-system-house-construction/818116/44 "2018-07-20T15:30:59Z")
A youtube video I saw pointed out that the NIST primary standards are already metric, they just convert to US units for customer convenience. So we’ve survived being metric so far. And like someone posted upthread, step one is to change the requirements so stud spacing is now the metric conversion of 16 inches. Then later you change the standard to round the numbers to something nice like 400mm. Similar to how the definition of light speed & meters changed from “about 3x10^8 m/s, relative to a primary standard metal meter rod”, to “light is exactly this number, and a meter is this many wavelengths of light” In radio and TV work, you have the similar kind of mish-mosh. One standard is “3-1/8 inch” line, but the actual product is now specced as 79.4 mm ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [July 20, 2018, 3:53pm UTC](https://boards.straightdope.com/t/more-questions-about-the-metric-system-house-construction/818116/45 "2018-07-20T15:53:26Z")
> [@Nava](#): > > The first time I went for a walk in a small Swedish town, I had to fight a grin when I recognized the roots of so much of US architecture 🙂 But your ideas of “good insulation” and mine… differ. Yes, Scandinavia would have the same conditions as the US northeast and Canada - plenty of wood and a need for insulation. In the last 30 years or so, Canadian standards have moved toward 2x6 external framing for R2000 insulation (6 inches of fibreglass not 4 inches). Before fibreglass insulation came along, “insulation” was a variable concept even in Canada with its colder winters. some older houses used sawdust. Fuel was cheap. There was a big industry in retrofitting much older houses by injecting urea-formaldehyde foam into old houses between the studs… until it was realized that improperly mixed foam off-gassed dangerous levels of formaldehyde. Nowadays even more tropical locations are seeing the benefits of installing good insulation to reduce the cost o air conditioning. ---
**Author:** ![Melbourne](https://avatars.discourse-cdn.com/v4/letter/m/b5e925/32.png) [@Melbourne](https://boards.straightdope.com/u/Melbourne)\ **Post date:** [July 21, 2018, 4:01am UTC](https://boards.straightdope.com/t/more-questions-about-the-metric-system-house-construction/818116/46 "2018-07-21T04:01:28Z")
> [@FluffyBob](#): > > Cabinet making is often all done in metric because frankly mm are a lot nicer to work with than '32s of an inch. I usually will do cabinet work in inches because that is the system the tape on my belt is in, and I don’t feel like going and digging out the metric tape. Oddly enough, in Aus cabinet making was one of the last hold-outs of traditional measures. People were buying 7’ bookshelves long after the people selling them had any general idea what the numbers meant. [Previous page](https://boards.straightdope.com/t/more-questions-about-the-metric-system-house-construction/818116.md?page=2)