A Worldbuilding Headache: Units of Measurement

Long ago, I lamented the difficulty of writing swear-words in secondary-world fantasy. Such words embody particular cultural values and norms, so when one tries to “translate” a story from an alien culture to our own… unless the secondary world has the same value-system and ideas about offensiveness as our primary world, there is going to be discrepancy and insincerity.

Today, I thought I would discuss a similar worldbuilding headache: units of measurement in a fantasy world.


Distance, time, weight, volume, currency, and so forth: these are everyday pieces of our own world, and from the point of view of our characters, such measurements are everyday pieces of theirs. So what are they exactly?

Distance, I think, is uniquely awkward. I am a 35 year-old New Zealand man – which means I am a child of the metric system. Metres, kilometres, centimetres, are all stuff I am comfortable with, and can visualise. The problem is that the metric system is a creation of the French Revolution – unless one is writing a pseudo-modern fantasy setting, it is going to feel out of place (science-fiction does not have this problem quite so much; the metric system is, after all, commonly used by scientists). The alternative, the Imperial measurement system – miles, inches, yards, and feet – feels like it buys into the Ye Old Western European Fantasy that has been done to death. It is all very well for J.R.R. Tolkien to use miles and inches, but we’re not in Middle-earth any more, and affecting a system that is (mostly) obsolete just so we can lend some faux Old World charm to a text feels wrong. The exception would be if I were writing American characters – but I generally don’t, and (for me), it would feel like I were altering colour to color or grey to gray without any real necessity.

I personally get around this by trying to avoid describing distances. Problem is, while I can do that (if I’m lucky) in short stories, longer works involve sinking my teeth into the proverbial bullet. Which is why, in Wise Phuul, the Viiminian Empire’s basic unit of length is the furlong (approximately 200 metres), so centifurlongs (2 metres) and millifurlongs (20 centimetres) are the measurement norm for Teltö and friends. Yes, it is utterly absurd – deliberately so – but it is also an attempt to make light of the crushing weight of history my characters find themselves buried under. In a setting less black-comedy-orientated, I would probably have to resort to miles, unless I can find something more setting-appropriate, which in a secondary world is a tough ask. I have also noticed that some other fantasy works make copious usage of leagues (3 miles/5 kilometres), which strikes me as an attempt to make something feel more authentically medieval without the modern American overtones of miles.

Time as a measurement is, I think, one we are generally stuck with, short of something more science fictional. Days, months, and years all carry with them “real world” baggage – the rotation of the Earth, the phases of the Moon, the Earth’s orbit around the Sun… does this mean that this supposed fantasy world is really our own? Can we not write a fantasy setting without the Moon as we know it? (certainly we can – Guy Gavriel Kay uses two moons in several books – but from memory it does not generate a unique measurement system to go with it). Even if one went to the trouble of making days and years different lengths, one would be reduced to translating that back into real-world days and years for reader convenience. Even George R.R. Martin’s variable and multi-year seasons do not interfere with the basic notion of a day or a year, which holds as much true in Westeros as it does Earth.

Weight and volume are, I think, the easiest to deal with, in the sense that they will likely come up less often, and there is arguably more room for fantastical flavour. The reader does not need to know how heavy, exactly, three dragonweight of oats are – it does not impact on the willing suspension of disbelief the way distance measurements do, and it does not require continual translation the way time measurements do. Which is all for the best, since otherwise one is stuck between kilograms and pounds in the same way as kilometres and miles.

That leaves currency, which is the sort of measurement system that is nastier than it looks. It is all very well to have Gold-Silver-Copper Standard units of value, with nice round numbers involved, until you realise that any form of bimetalic currency runs into Gresham’s Law, and that a hypothetical trimetalic system would be Gresham’s Law on steroids. Meanwhile, despite the apparent arbitrary nature of pre-decimal British currency, it actually made sense in terms of permitting easy calculation of fractions – there was method to its madness, in that 12 pennies to a shilling and 20 shillings in a pound makes for even sub-division. Harry Potter’s 17 Sickles to the Galleon and 29 Knuts to the Sickle is (deliberately) whimsical, but would be nasty in practice, because 17 and 29 are both prime numbers, and thus cannot be factorised in the way that 12 or 20 can. Wise Phuul’s currency system (113 bits to the mark) similarly falls foul of the prime problem, but in my defence, it’s close enough to decimal currency that I think one could manage rough guesstimates. And I was going for weirdness, damn it.

Units of measurement is something that can only ever be an issue for worldbuilding, as unlike swearing it does not play a role in depicting character, and it is seriously unlikely to impact either theme or plot. It is, however, the sort of thing I think needs to be thought about, at least for longer fantasy works. Distance, time, et cetera, exist in a secondary world, and the characters are going to know how these things are measured in-universe – their writer probably ought to know too.

4 thoughts on “A Worldbuilding Headache: Units of Measurement

  1. Having separate units for time and distance is a cultural artifact. It’s not weird to say that my house is an hour away from yours, since it’s obvious what mode of transportation is assumed. I bet a writer could have a lot of fun by screwing up the assumptions.


    • Edmund Spenser, in ‘The Faerie Queene’, already needed in the 1500s to find suitably archaic-sounding units of length. In the infamous ‘wanton wrestling’ scene (FQ II, XII, 62-63) they are cubits. Frodo gauges height in fathoms but Sam measures rope in ells (LOTR IV, I)


  2. Another fine, very thoughtful article. 🙂

    It also feels rather timely, as it wasn’t that long ago that I was devising various measurement units for my own setting. They have an early industrial revolution going on, but there has been no ideological and political upheaval similar to the French revolution or the Napoleonic Wars. There are some trains of thought on standardising things in the academic and science worlds, but no one has yet come up with anything approaching an in-universe metric system. Some countries have attempted to standardise some widespread measurement units instead, but these are regional efforts at best. Given that my primary focus is on a small country, and their local standards, the units I have nailed down so far mostly pertain to the systems they have in place, but not necessarily all other countries, including the neighbouring ones.

    It’s always a double-edged sword when fantasy writers try to avoid real world terms and come up with reasonable equivalents that fit the setting. Get too clumsy with the naming or the rationale behind the units, and suspension of disbelief starts getting affected just as much as if the author just lazily used metric, with no pause for thought. Thinking about this often in recent years, I tend to stick to the personal maxim of “make things sound and be understandable to a degree that is familiar, but also has a clear touch of the alien”. In short, “familiar, but alien”, which I think is a reasonable approach for a closely historically inspired, quasi early modern setting like mine. This extended not only to units of measurement, or the calendar used in my setting, but also to little details like the names (and structure) of law enforcement ranks. I wanted to evoke an alternate evolution of names, independent of the real world, and based on that universe’s own traditions (including folk vocabulary), but not make it different to the point where everyone would be lost. I’m fairly satisfied with the current measurement units I have, and their occassional quirks (including obvious imprecisions, at least from a modern scientific point of view), but there is still for improvement in the future. Names and dimensions for units of length, volume, etc., were the easier ones for me. Temperature measurements were harder, but I figured the setting’s naturalists would base them around the boiling points of substances, and the rest would be imprecise folk measurements (derived from things like the thawing of snow or the onset of frost, etc.). Time measurement units and naval measurement units were the difficult bits, they took me a while to nail down. In the case of time measurements, virtually all of them are based on folk tradition and rather imprecise standards, whether they are land-based (e.g. often measured by average time it takes to say a type of in-universe prayer) or ship-based (mostly based around the ringing of ship bells and guard duty shifts on ships). As I come from a landlocked county, naval measurements were a bit tricky. They include distance and speed measurements, and though I like the ones I made up, I am still on the fence on whether to include knots as in the real world. Given the technology of my universe, knots would certainly plausible, even if their standard would no doubt differ from what we nowadays call a knot. For the time being, I have not included them in the setting, but who knows ? I might make some version of them canon, someday.

    You got me with Gresham’s Law ! That is something that authors don’t pay that much attention to (though as stated, in most cases, the nitty-gritty of currency usage and exchange rates doesn’t come up in stories).

    Now I feel like writing a short story in my developing setting, where there’s some miscommunication about units of measurement in some device or new invention, and it has major repercussions. 🙂 Could be a fun self-imposed writing challenge.


  3. Edmund Spenser, in ‘The Faerie Queene’, already needed in the 1500s to find suitably archaic-sounding units of length. In the infamous ‘wanton wrestling’ scene (FQ II, XII, 62-63) they are cubits. In LOTR Frodo gauges height in fathoms but Sam measures rope in ells (IV, I)


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