u/nayuki

Forget about the wider world for a minute. I got myself into 3D printing less than a year ago. I design models, run and tweak slicer software, shop for machines and components (nozzles, etc.) and supplies (filaments, etc.), and watch way too many explainer videos from many online creators.

When I step back from various individual topics in 3D printing, I notice something in the big picture that's easily taken for granted: Everyone uses metric units when describing 3D printing techniques and products, and even use the same unit in almost all domains (with minor variations like g/kg, m/mm/μm). It doesn't matter if the designer, product, or YouTuber is from America, Europe, or Asia - the units are always the same, and I barely know the country of origin unless I dig into details. This is so radically different from older industries and practices, like when you have to worry about whether to use an inch ruler or centimetre ruler, what a "tatami mat" is in Japanese real estate, what a short ton vs. long ton versus metric ton is when shipping large goods, whether you're buying gallons or litres of fuel, whether a recipe is in °C or °F, etc.

So if you're involved in 3D printing, you get a firsthand experience of what it's like when everyone internationally uses the same units, everyone participates in the same discussion and shop in the same marketplace, and you don't have to convert any numbers and units. It's such a breath of fresh air, and I wish other industries would unify their measurements in this way.

Keep in mind that 3D printing is about 20-ish years old, depending on how you look at the history of consumer products vs. industrial products vs. research prototypes. It had the opportunity to start fresh, without much baggage of traditional units and practices, and was born into the Internet-connected world. In terms of measurement units, I think this industry absolutely made the right choices, despite being surrounded by so many pre-existing industries that use non-metric units and continue to make the bad choice of not transitioning to metric.

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Here are some examples of real quantities used in 3D printing and described in metric units (left side), versus my hypothetical caricature (based on other industries) of what it would look like if US Customary units are involved (right side):

• Layer height: 0.07 mm, 0.15 mm, 0.25 mm - versus - 3 thou, 6 thou, 10 thou, 3/1024″ (LMAO), 3/512″, 5/512″.
• Nozzle diameter: {0.2, 0.4, 0.6} mm - versus - 0.008″, 0.015″, 0.025″.
• Spool of filament: 1 kg, 3 kg - versus 2.2 lb, 6.6 lb, 2 lb 3 oz, 6 lb 10 oz. (You could choose to sell a nice round number of pounds, but then it would have ugly decimals in kilograms.)
• Random masses of printed objects (slicer software can calculate and show, or physically weigh after printing): {23.7, 98.9, 230, 664} grams - versus - {0.8, 3.5, 8.1, 23.4} oz, {0.05, 0.22, 0.51, 1.46} lb, 1 lb 7.4 oz.
• Random lengths of filament consumed (slicer software can calculate and show): {6.15, 72.7, 364} metres - versus - {242, 2862, 14331}″, {20′ 2″, 238′ 6″, 1194′ 3″}, {20.2, 238.5, 1194.2}′, {6yd 2′ 2″, 79yd 1′ 6″, 398yd 3″} (I thought USC lovers love mixed units?), {6.73, 79.5, 398} yd.
• Build plate printable dimensions: 250 mm × 210 mm = 52 500 mm² - versus - approximately 10″ × 8″ = 80 in², 9 27/32″ × 8 1/4″ = 81.2 in² = 0.564 sq ft.
• Build volume: 153.4 mm × 87 mm × 165 mm = 2 202 057 mm³ = 2.202 L - versus - 6.03″ × 3.43″ × 6.50″ = 134.44 in³ = 74.5 US fl oz = 9.31 US cup = 2.33 US qt = 0.581 US gal.
• Chamber, bed, nozzle temperature: {50, 100, 230} °C - versus - {120, 210, 445} °F.

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Extra topics tangentially related:

• I'm glad 3D printing chose millimetres, not centimetre, as the unit of length - because it scales by a power of 1000 from the metre, just like the micrometre, nanometre, kilometre, etc. Before 3D printing existed, the precedent is that serious engineering and metal machining already use millimetres, not centimetres. Advocates for mm over cm include Pat Naughtin (video and long PDF) and the Metric Maven. I could write a full-length post about why centimetres are bad; there really is a lot to say about it.
• I talk about all aspects of my 3D modeling in millimetres exclusively - "this needs a 5.8 mm diameter hole", "the overall part is 200 mm long". Other people might talk about these aspects in customary units, like "1/4-inch hole", "needs 3 inches of clearance", which I find mildly annoying. But even then, these people will never refer to the layer height or nozzle diameter in decimal inches - which is good for the 3D printing community, but inconsistent with their other habits.
• Typical acceleration numbers are written like "20 000 mm/s²", which is equal to 20 m/s². The former isn't wrong, but it's more digits than necessary. And I've seen some people refer to it as "20K mm/s²", which is wrong in multiple ways. This is analogous to the questionable practice of labeling power banks as "10 000 mAh" instead of "10 A⋅h".
• My previous observation about exclusively using degrees Celsius in 3D printing: https://www.reddit.com/r/Metric/comments/1qumhtn/personal_computers_and_3d_printers_use_celsius/