Units

Rowlett	Tower Grain	Troy Grain	Gram	Tower Ounce	Troy Ounce	Avoir. Ounce	Tower Pound	Troy Pound	Merchant Pound	London Pound	Avoir. Pound
Tower Pound	7680	5400	349.914	12	11¹⁄₄	12¹²⁄₃₅	1	¹⁵⁄₁₆	⁴⁄₅	³⁄₄	²⁷⁄₃₅
Troy Pound	8192	5760	373.242	12⁴⁄₅	12	13²⁹⁄₁₇₅	¹⁶⁄₁₅	1	⁶⁴⁄₇₅	⁴⁄₅	¹⁴⁴⁄₁₇₅
Merchant Pound	9600	6750	437.393	15	14¹⁄₁₆	15³⁄₇	⁵⁄₄	⁷⁵⁄₆₄	1	¹⁵⁄₁₆	²⁷⁄₂₈
London Pound	10240	7200	466.552	16	15	16¹⁶⁄₃₅	⁴⁄₃	⁵⁄₄	¹⁶⁄₁₅	1	³⁶⁄₃₅
Avoir. Pound	9955⁵⁄₉	7000	453.592	15⁵⁄₉	14⁷⁄₁₂	16	³⁵⁄₂₇	¹⁷⁵⁄₁₄₄	²⁸⁄₂₇	³⁵⁄₃₆	1
Tower Ounce	640	450	29.160	1	¹⁵⁄₁₆	³⁶⁄₃₅	¹⁄₁₂	⁵⁄₆₄	¹⁄₁₅	¹⁄₁₆	⁹⁄₁₄₀
Troy Ounce	682²⁄₃	480	31.103	¹⁶⁄₁₅	1	¹⁹²⁄₁₇₅	⁴⁄₄₅	¹⁄₁₂	¹⁶⁄₂₂₅	¹⁄₁₅	¹²⁄₁₇₅
Avoir. Ounce	622²⁄₉	437¹⁄₂	28.350	³⁵⁄₃₆	¹⁷⁵⁄₁₉₂	1	³⁵⁄₄₃₂	⁶⁄₇₉	⁷⁄₁₀₈	³⁵⁄₅₇₆	¹⁄₁₆

AD&D

• 240 p = 12 s = 2 C = 1 £ = ¹⁄₅ G (pre-decimal Britain)
• 200 cp = __ sp = 2 ep = 1 gp = 1/5 pp = 1.6 avoir. oz.
• 10 gp = 1 pound

• Feet =
• 1 inch (1″) = 10 feet (10′) indoors = 10 yards (30′) outdoors
• League = 3 miles
• 186,000 miles = 1 light second ^(PHB-116)

miles

Unit	Length (m)	Notes
kilometre	1,000
mille passus	1,479.5	1,000 passus (5,000 pedes)
mille passus	1,480	1,000 passus (5,000 pedes)
mile, imperialUK	1,609.339	5,280 imperial feet
mile, international	1,609.344	5,280 international feet
mile, surveyUS	1,609.347	5,280 survey feet
mile (AD&D)	1,611.787	186,000 miles = 1 light second
mile (d20)	1,828.8	6,000 feet
mile, nauticalInt.	1,852	1⁄60° lattitude
mile, AdmiraltyUK	1,853.184	6,080 Imperial feet
mile, nauticalUS	1,853.245	6,080.20 statute feet
light-second	299,792,458	186,282.4 statute miles

1 cubic-pes of water = 64 lībrae

1 foot = 12 inches

3 feet = 1 yard

5 feet = 1 pace

6 feet = 1 fathom

5000 feet = 1 mile (land)

6000 feet = 1 mile (nautical)

1 furlong = 10 chains = 40 rods = 1000 links

Other units

A d20/D&D mile (𝗆𝗂^𝖣) is 6,000 feet, and thus apparently a fantasy equivalent to the ≈ 6,076-foot nautical mile rather than the 5,280-foot land mile.

A nautical mile (𝖭𝗆𝗂) is one minute of latitude (1′ = ‌¹⁄₆₀ °), making Earth’s meridional circumference 21,600 𝖭𝗆𝗂. Since Earth is not a perfect sphere, the actual length of a minute of latitude varies between 1,813 𝗆 and 1,861 𝗆 with a de jure average of 1,852 𝗆 (≈ 6076.12-ft).

The original intent for the meter was to be one ten-millionth of 90° latitude, such that 40,000 ㎞ would equal Earth’s meridional circumference. The best measurements of the 1800s were slightly off and Earth’s actual m. circ. in standard meters is ≈ 40,008 ㎞.

From this one can extrapolate that a standard D&D fantasy world could be:

1. a 21,600 𝖭𝗆𝗂 ≈ 40,008 ㎞ m.circ. spheroid like Earth,
2. a 21,600 𝗆𝗂^𝖣 ≈ 39,502 ㎞ m.circ. spheroid with 2½% less surface area than Earth, or
3. a 21,600 𝗆𝗂^𝖣 = 40,000 ㎞ m.circ. sphere with D&D feet/inches etc. 1¼% longer than standard feet/inches.

Greek

1 million (∼mile) = 5,000 podes

1 stade (∼furlong) = 600 podes

1 plethron = 100 podes (∼feet)

Roman

1 mille passus (∼mile) = 8 stadia = 1,000 passus = 6,000 pedes

1 stadium (∼furlong) = 125 passus = 625 pedes

1 passus (∼pace) = 5 pedes (∼feet)

The minum (♏︎) was originally defined in 1809 by Timothy Lane, FRS as ‌¹⁄₆₁₄₄₀ of the [Queen Ann] wine gallon (i.e. 231 in³ or 58,176 gr.t. H₂O at 29.52″ Hg_63 °F) Pharmacopoeia In the UK, the minim was redefined as ‌¹⁄₇₆₈₀₀ of the new Imperial gallon (10 lb. H₂O at 62 °F) 1824 act The Weights and Measures Act of 1878 (41 & 42 Vict. c 49)