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Description

Conversion of units
1
Conversion of units
Conversion of units refers to conversion factors between different units of measurement for the same quantity.
Techniques
Process
The process of conversion depends on the specific situation and the intended purpose. This may be governed by regulation, contract, Technical specifications or other published standards. Engineering judgment may include such factors as: ã ã ã ã The precision and accuracy of measurement and the associated uncertainty of meas

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Conversion of units1
Conversion of units
Conversion of units
refers to
conversion factors
between different units of measurement for the same quantity.
Techniques
Process
The process of conversion depends on the specific situation and the intended purpose. This may be governed byregulation, contract, Technical specifications or other published standards. Engineering judgment may include suchfactors as:ãThe precision and accuracy of measurement and the associated uncertainty of measurementãThe statistical confidence interval or tolerance interval of the initial measurementãThe number of significant figures of the measurementãThe intended use of the measurement including the engineering tolerancesSome conversions from one system of units to another need to be exact, without increasing or decreasing theprecision of the first measurement. This is sometimes called
soft conversion
. It does not involve changing thephysical configuration of the item being measured.By contrast, a
hard conversion
or an
adaptive conversion
may not be exactly equivalent. It changes the measurementto convenient and workable numbers and units in the new system. It sometimes involves a slightly differentconfiguration, or size substitution, of the item.
Multiplication Factors
Conversion between units in the metric system can be discerned by their prefixes (for example, 1 kilogram =1000 grams, 1 milligram = 0.001 grams) and are thus not listed in this article. Exceptions are made if the unit iscommonly known by another name (for example, 1 micron = 10
−
6
metre).
Table Ordering
Within each table, the units are listed alphabetically, and the SI units (base or derived) are highlighted.
Tables of conversion factors
This article gives lists of conversion factors for each of a number of physical quantities, which are listed in the index.For each physical quantity, a number of different units (some only of historical interest) are shown and expressed interms of the corresponding SI unit.
Conversion of units2
Legend
Symbol Definition
≡
exactly equal to
≈
approximately equal to
digits
indicates that digits repeat infinitely (e.g. 8.294369 corresponds to 8.294369369369369
…
)
(H)
of chiefly historical interest
LengthLength
Name of unit Symbol Definition Relation to SI units
ångströmÅ
≡
1 × 10
−
10
m
≡
0.1 nmastronomical unitAU
≈
Distance from Earth to Sun
≈
149597871464 m[1]barleycorn (H)=
⅓
in (see note above about rounding)
≈
8.46×10
−
3
mbohr, atomic unit of lengtha
0
≡
Bohr radius of hydrogen
≈
5.2917720859 × 10
−
11
± 3.6 × 10
−
20
m[2]cable length (Imperial)
≡
608 ft
≈
185.3184 mcable length(International)
≡
1/10 nmi
≡
185.2 mcable length (U.S.)
≡
720 ft= 219.456 mchain (Gunter's;Surveyor's)ch
≡
66 ft(US)
≡
4 rods[3]
≈
20.11684 mcubit (H)
≡
Distance from fingers to elbow
≈
18 in
≈
0.5 mell (H)ell
≡
45 in[4](In England usually)= 1.143 mfathomfm
≡
6 ft[4]= 1.8288 mfermifm
≡
1 × 10
−
15
m[4]
≡
1 × 10
−
15
mfinger
≡
7/8 in= 0.022225 mfinger (cloth)
≡
4½ in= 0.1143 mfoot (Benoît) (H)ft (Ben)
≈
0.304799735 mfoot (Clarke's; Cape) (H)ft (Cla)
≈
0.3047972654 mfoot (Indian) (H)ft Ind
≈
0.304799514 mfoot (International)ft
≡
1/3 yd
≡
0.3048 m
≡
12 inches
≡
0.3048 mfoot (Sear's) (H)ft (Sear)
≈
0.30479947 mfoot (U.S. Survey)ft (US)
≡
1200
⁄
3937
m[5]
≈
0.304800610 mfrench; charriereF
≡
1
⁄
3
mm= 0.3 ×10
−
3
mfurlongfur
≡
10 chains = 660 ft = 220 yd[4]= 201.168 mhand
≡
4 in[4]
≡
0.1016 m
Conversion of units3
inch (International)in
≡
1/36 yd
≡
1/12 ft
≡
0.0254 mleague (land)lea
≡
3 US Statute miles[3]= 4828.032 mlight-day
≡
24 light-hours
≡
2.59020683712 × 10
13
mlight-hour
≡
60 light-minutes
≡
1.0792528488 × 10
12
mlight-minute
≡
60 light-seconds
≡
1.798754748 × 10
10
mlight-second
≡
Distance light travels in one second in vacuum
≡
299792458 mlight-yearly
≡
Distance light travels in vacuum in 365.25 days[6]= 9.4607304725810 × 10
15
mlineln
≡
1/12 in[7]= 0.002116 mlink (Gunter's; Surveyor's)lnk
≡
1/100 ch[4]
≡
0.66 ft
≡
7.92in= 0.201168 mlink (Ramsden's;Engineer's)lnk
≡
1 ft[4]= 0.3048 mmetre (SI base unit)m
≡
Distance light travels in
1
⁄
299792458
of a second invacuum.[8]
≈
1
⁄
10000000
of the distance from equator to pole.
≡
1 mmickey
≡
1
⁄
200
in= 1.27 × 10
−
4
mmicronµ
≡
1 × 10
−
6
mmil; thoumil
≡
1 × 10
−
3
in
≡
2.54 × 10
−
5
mmil (Sweden and Norway)mil
≡
10 km= 10000 mmile (geographical) (H)
≡
6082 ft= 1853.7936 mmile (international)mi
≡
80 chains
≡
5280 ft
≡
1760 yd
≡
1609.344 mmile (tactical or data)
≡
6000 ft
≡
1828.8 mmile (telegraph) (H)mi
≡
6087 ft= 1855.3176 mmile (U.S. Survey)mi
≡
5280 US Survey feet
≡
(5280 ×
1200
⁄
3937
) m
≈
1609.347219 mnail (cloth)
≡
2¼ in[4]= 0.057 15 mnanometernm
≡
1 × 10
−
9
m
≡
1 × 10
−
9
mnautical leagueNL; nl
≡
3 nmi[4]= 5556 mnautical mile (Admiralty)NM (Adm); nmi(Adm)= 6080 ft= 1853.184 mnautical mile(international)NM; nmi
≡
1852 m[9]
≡
1852 mnautical mile (US pre1954)
≡
1853.248 m
≡
1853.248 mpace
≡
2.5 ft[4]= 0.762 mpalm
≡
3 in[4]= 0.0762 mparsecpcDistance of star with
par
allax shift of one arc
sec
ondfrom a base of one astronomical unit
≈
3.085 677 82×10
16
± 6×10
6
m[10]pica
≡
12 pointsDependent on point measures.
Conversion of units4
point (American, English)[11] [12]pt
≡
1/72.272 in
≈
0.000 351 450 mpoint (Didot; European)[12] [13]pt
≡
1/12 × 1/72 of pied du roi;After 1878:
≡
5/133 cm
≈
0.000 375 97 m;After 1878:
≈
0.000 375 939 85 mpoint (PostScript)[11]pt
≡
1/72 in= 0.000 352 7 mpoint (TeX)[11]pt
≡
1/72.27 in= 0.000 351 4598 mquarter
≡
¼ yd= 0.2286 mrod; pole; perch (H)rd
≡
16½ ft= 5.0292 mrope (H)rope
≡
20 ft[4]= 6.096 mspan (H)
≡
9 in[4]= 0.2286 mspat[14]
≡
1×10
12
mstick (H)
≡
2 in= 0.0508 mstigma; bicron(picometre)pm
≡
1×10
−
12
mtwiptwp
≡
1/1440 in= 1.7638×10
−
5
mx unit; siegbahnxu
≈
1.0021×10
−
13
m[4]yard (International)yd
≡
0.9144 m[5]
≡
3 ft
≡
36 in
≡
0.9144 m
AreaArea
Name of unit Symbol Definition Relation to SI units
acre (international)ac
≡
1 ch × 10 ch = 4840 sq yd
≡
4 046.856 4224 m
2
acre (U. S. survey)ac
≡
10 sq ch = 4840 sq yd, also 43560 sq ft.
≈
4 046.873 m
2
[15]area
≡
100 m
2
= 100 m
2
barnb
≡
10
−
28
m
2
= 10
−
28
m
2
barony
≡
4000 ac
≈
1.618 742×10
7
m
2
boardbd
≡
1 in × 1 ft= 7.741 92×10
−
3
m
2
boiler horsepower equivalent direct radiationbhp EDR
≡
(1 ft
2
) (1 bhp) / (240 BTU
IT
/h)
≈
12.958 174 m
2
circular inchcirc in
≡
π/4 sq in
≈
5.067 075×10
−
4
m
2
circular mil; circular thoucirc mil
≡
π/4 mil
2
≈
5.067 075×10
−
10
m
2
cord
≡
192 bd= 1.486 448 64 m
2
dunam
≡
1 000 m
2
= 1 000 m
2
guntha
≡
121 sq yd
≈
101.17 m
2
hectareha
≡
10 000 m
2
≡
10 000 m
2

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