"Here, laddie," the dwarf says handing you a small cup, "Have a noggin of ale!"
Basic Information
Here is a list of some units of measurement and their equivalents in the US and Metric Systems.
Quantities
Brace/Pair/Couple: 2
Dozen: 12
Score: 20
Gross: 144
Mole: 6.02214076 x 1023 — usually applied only to very small things such as atoms or molecules, used for comparing elements by mass
Lakh: 100,000
Crore: 10 million
Sagan: at least 4 billion. Humorous unit.
Weights
Dalton: 1.66053906892(52)×10−27 kg — roughly the mass of a proton or neutron, the usual unit for atomic weight. Natural unit.
Pennyweight: 1/20 ounce (1.555 g)
Dram: 60 grains (3.888 g)
Clove: 8 lbs. (3.628 kg)
Stone: 14 lbs. (6.35 kg) — human weight is sometimes given in stone.
Fardel: 32 lbs. — "Who would fardels bear?"
Slug1: 32.1740 lb (14.59390 kg)
Talent (Attic): ~26 kg (57 lb)
Talent (Roman): ~32.3 kg (71 lb),
Talent (Babylonian)2: 30.3 kilograms (67 lb).
Talent (Heavy Common)3:58.9 kilograms (130 lb)
Firkin: 25 kg/56 lbs (also 9 gallons/41 L of volume)
Hundredweight: 112 lbs. (50.802 kg)
Earth mass: 5.9722×1024 kg — mass of the planet Earth.
Jupiter mass: 1.9 ×1027 kg — mass of the planet Jupiter.
Solar mass: 2 x 1030 kg — approximately the mass of the Sun.
Chandrasekar limit: ~1.4 solar masses — maximum mass of a stable white dwarf star. Natural unit.
Linear Measurement
Planck length: 1.62 x 10-35 m — possibly the smallest length meaningfully measurable due to quantum effects. Natural unit.
Angstrom: 10-10 m — close to the width of a hydrogen atom.
Barleycorn: 1/3 inch (0.8 cm) — an inch was at one time defined as the length of three grains of barley
Palm: 3 inches (7.62 cm)
Hand: 4 inches (10.16 cm) —the width of a hand; frequently used in measuring the height of horses.
Span: 9 inches (22.86 cm) — the width of a stretched out hand from pinky to thumb.
Cubit: about 18 inches (about 0.5 m) — the distance between the elbow and the tip of the finger; a common unit of measurement in the Bible
Ell: 45 inches (1.143 m) —Medieval unit used for measuring cloth
Smoot: 5 feet, 7 inches (170 cm) — height in 1958 of a specific future ANSI and ISO president. Humorous unit.
Fathom: 6 feet (1.8288 m) — Nautical measure of depth; the length of a man's outstretched arms.
Rod: 16.5 feet (5.029 m) — Surveying measure
Chain: 66 feet (20.12 m) — 4 rods. Surveying measure
Furlong: 660 feet (201.168 m) — 10 chains. Surveying measure
Cable (Imperial): 608 feet (185.318 m) — Nautical measure (there are different definitions of a cable: International cable is slightly shorter and US cable is considerably longer)
Li: 1640 feet (500 m)
League: 3 miles (4.828 km)
Light second: 186,000 miles — distance light travels in one second
Astronomical unit: 1.496 x 1011 meters — average distance between the Earth and the Sun
Parsec: 3.26 light years
Angle
Minute: 1/60 degree
Second: 1/60 minute
Third: 1/60 second
Gradian: 9/10 degree — alternative unit devised by the French Revolutionary government, 1/100 of a right angle. The original definition of a kilometer was 1 gradian on the Earth's surface.
Radian: 180/pi degrees — the radius of a circle laid along its circumference.
Area
Barn: 10−28 m2 — approximate cross-section of a uranium nucleus, used in particle accelerators
Guntha: 121 sq. yard/101.17 square m
Hide: 120 acres/12100 square m
Volume
Noggin: 1/4 pint
Pin: 4 gallons/15 L
Bushel: 8 gallons/72 L
Firkin: 8 gallons/30 L
Kilderkin: 16 gallons/59 L
Rundlet: 18 gallons/68 L
Barrel: 32 gallons/118 L
Tierce: 42 gallons/159 L
Hogshead: 63 gallons/238 L — 2 barrels
Puncheon: 84 gallons/318 L
Butt, Pipe: 126 gallons/477 L —2 hogsheads
Tun: 252 gallons/954 L — 4 hogsheads
Time
Planck time: 5.39 x 10-44 seconds — time in which light travels one Planck length. Natural unit.
Decimal minute: 86.4 seconds — French Revolutionary unit, one one-thousandth of a day
Decimal hour: 2 hours, 24 minutes — French Revolutionary unit, one tenth of a day
Fortnight: 14 days
Divine year: 360 solar years
Sothic cycle: ~1460 solar years — Ancient Egyptian calendar period, time in which the 365-day year loses enough time to resynchronize.
Galactic year: 250 million years — one revolution of the Milky Way galaxy.
Kalpa (Hindu): 4.32 billion years — the lifespan of a universe in Hindu cosmology.
Kalpa (Buddhist, regular): ~16 million years — definition is somewhat allegorical; larger small, medium, and great kalpas are defined in terms of it.
Concentration
Part per thousand/million/billion
Molar: 1 mole/liter
Energy
Electron volt: 1.6×10−19 joules — used in particle accelerators, particle masses are sometimes given in meV.
Erg: 1 x 10-7 joules
Calorie: 4.1868 joules — energy needed to heat 1mL of water at STP by 1°C
Foot-pound: ~1.355 joules
British thermal unit: ~1055 joules
Dietary calorie: 4184 J — energy needed to heat 1L of water by 1°C; also roughly 1/2000 of an adult human's daily resting energy consumption.
Kilowatt-hour: 3.6×106 joules
Gallon gasoline: 1.213×108 joules
Ton TNT: 4.184 gigajoules
Kilogram mass-energy equivalence: ~90 petajoules
Miscellaneous
Millihelen: the amount of beauty that can launch one ship. Humourous unit.
Candela: A brightness roughly equivalent to a wax candle.
Sources
Game and Story Use
- Using setting-appropriate units of measurement to describe things can help give flavor to a setting.
- Just be sure to also give a more familiar conversion, so that the players know what you're talking about.
- For example: The giant stands over six cubits high, at least nine feet tall.
- The submarine surfaces a cable length from your ship; about 180 meters
- The dwarf has a beard three ells long, and it trails over ten feet behind him.
- Just be sure to also give a more familiar conversion, so that the players know what you're talking about.
- Plenty of fun to be had dealing with different measuring systems.
- One country's talents are a different size than another's, and both accuse the other of being cheats.
- One scientist thinks in miles per hour, while another thinks in meters per second. When one gives a number without units, the other hears a completely different number close enough to not be obviously wrong. (Spacecraft have been lost this way.)
- Worse still, both think, work and write in miles per hour, but come from cultures with a different length of mile…
- Chaos erupts as a country standardizes its measures, or adopts a neighbor's system. While it might make industry and commerce easier in the long run, right now everyone's just confused.
- Similar confusion might happen where the same name is given to units of different dimensions. "Is a koku of beer volume, energy, or money?" (traditionally it's the amount of rice required to feed one person for a year … which is itself open to debate but is currently considered to be 180L). And don't ask the Indians how much a lakh is unless you have a lot of time on your hands (as above, it's officially 100,000 units, but arguments still ensue).
- When there's a new phenomenon, feel free to invent your own units to describe it. "The merlin is defined as the theoretical minimum amount of mana necessary to power an illumination spell at one candela…"
- Annoyingly some of these measurements may be a little … unstable … in the pre-modern era. A hide, for example was originally enough land to support one peasant (and his dependants) and the actual size could depend on the quality of the land and in some cultures measures of length could be based on the size of the current ruler rather than a fixed measure.
- Having someone use really big or really small units is a handy way of driving home that you're not operating on a human scale anymore. No more talking about feet or miles of movement, once you activate your FTL drive each hex on the map is now a parsec.
- Also watch for the people who misuse units when trying to sound clever: completing a journey in "less than five parsecs" or having it take "light years of time" are well known examples.
- A natural-units system, where each unit is defined in terms of fundamental physics, may be useful for communicating with aliens - but requires some very advanced science to create, and most fundamental physical properties don't translate well to a human scale.
- A major political upheaval might bring with it a change in measuring systems, whether changing the "foot" to match the current king's foot or the (possibly excessive) metrification during the French Revolution. Which units you use may be taken as a sign of allegiances, whether you intended it that way or not.
Units conversion site : Unit Converter