Simetrium
A passport for every unit of measurement. In 36 languages.
Main entrance · search units, quantities and pairs
Most asked
7
base units
22
named derived units
36
translation languages
00 · New on the site
Fresh unit sheets
author's unit · audience time
Attention minuteviews versus minutes of attentionmedicine · mass over height squared
Body mass indexone index for a country and for your neighbournon-SI · a count of seconds
Unix time and ISO 8601 notationa limit set by the width of the machine wordmycology · ring growth rate
Fairy ringsthe ring of mushrooms gets wider every yearmycology · carbon to the fungus
Mycorrhizathe tree pays the fungus in sugar for nitrogenmycology · mass per area
Mycelium and fruit bodythe fungus underground outweighs the mushrooms in the basketmaritime transport · capacity
TEUone box, one TEU: containers, ships and roadsfinance · fraction per year
Annual percentage rateone rate, three numbers: APR, APY and total costnon-SI · automatic identification
QR codea square a camera reads from any anglenon-SI · automatic identification
Barcodestripes a checkout reads in a split secondspore launch speed · metre per second
Spore dischargehow a mushroom shoots its spores into the gapradial growth rate · millimetre per day
Mycelium growthwhy the colony grows at a steady pacespore length · micrometre, Q = L/W
Spore size and the Q ratiothe dust that names the mushroomcore temperature · degree Celsius
Body temperaturethe 37 degrees that cooled downoxyhaemoglobin fraction · pulse
Pulse oximetrytwo lights that see blood through a finger
Attention minuteviews versus minutes of attentionmedicine · mass over height squaredBody mass indexone index for a country and for your neighbournon-SI · a count of secondsUnix time and ISO 8601 notationa limit set by the width of the machine wordmycology · ring growth rateFairy ringsthe ring of mushrooms gets wider every yearmycology · carbon to the fungusMycorrhizathe tree pays the fungus in sugar for nitrogenmycology · mass per areaMycelium and fruit bodythe fungus underground outweighs the mushrooms in the basketmaritime transport · capacityTEUone box, one TEU: containers, ships and roadsfinance · fraction per yearAnnual percentage rateone rate, three numbers: APR, APY and total costnon-SI · automatic identificationQR codea square a camera reads from any anglenon-SI · automatic identificationBarcodestripes a checkout reads in a split secondspore launch speed · metre per secondSpore dischargehow a mushroom shoots its spores into the gapradial growth rate · millimetre per dayMycelium growthwhy the colony grows at a steady pacespore length · micrometre, Q = L/WSpore size and the Q ratiothe dust that names the mushroomcore temperature · degree CelsiusBody temperaturethe 37 degrees that cooled downoxyhaemoglobin fraction · pulsePulse oximetrytwo lights that see blood through a finger01 · Universal converter
Convert one into another
The same mechanism that sits in every unit passport, here in universal form: pick the quantity first, then the pair of units. Factors follow the SI Brochure and NIST SP 811, with no rounding in the definitions.
Quantity: length
base: metre
1 m = 3.280839895 ft (exact, by the 1959 agreement)
the foundation · 7 units
The seven SI base units
02 · Catalogue of quantities
Catalogue of quantities
N
derived
force
9 units
Pa
derived
pressure
16 units
J
derived
energy
14 units
W
derived
power
9 units
Hz
derived
frequency
6 units
V
derived
voltage
5 units
Ω
derived
resistance
4 units
C
derived
charge
4 units
T
derived
magnetic flux density
5 units
lx
derived
illuminance
3 units
Bq
derived
radioactivity
3 units
m³
non-SI
volume
26 units
m²
non-SI
area
9 units
m/s
non-SI
speed
6 units
°
non-SI
angle
7 units
bit
non-SI
data
18 units
Fderived
electrical capacitance
12 units
Sderived
electrical conductance
13 units
Wbderived
magnetic flux
12 units
Hderived
inductance
10 units
°Cderived
temperature
8 units
lmderived
luminous flux
9 units
Gyderived
absorbed dose
12 units
Svderived
equivalent dose
11 units
katderived
catalytic activity
11 units
radderived
plane angle
13 units
srderived
solid angle
11 units
l/100km
non-SI
fuel consumption
4 units
dB
non-SI
level
3 units
pud
archive
Russian measures
12 units
fur
archive
old English
9 units
erg
archive
CGS
8 units
Ci
archive
old radiology
5 units
03 · Everyday pairs
What people convert every day
Series · Drafting and CAD
Sheets for the draughtsman
dimensionless · drafting and CAD
Drawing scalea number you assign, not measuredimensionless · drafting and CAD
Scale in CADa scale that lives in the viewport, not in the partunit code · drafting and CAD
Drawing unitsa number that doesn’t know what it is measured inlength on paper · drafting and CAD
Lineweighta thickness that shrinks with the sheetlength on paper · drafting and CAD
Text heighta letter measured by its capitallength · drafting and CAD
Thread pitchthe number of threads that decides whether the nut will go ondimensionless · drafting and CAD
Tapera ratio that holds a drill without a keydimensionless · drafting and CAD
Slopethe rise along a length that makes a wedge hold itselflength · drafting and CAD
Weld legthe side you measure and the height that holdsclearance and interference · drafting and CAD
Fittwo tolerance zones with the clearance living between themplane angle · drafting, CAD and surveying
Gonan angle split into a hundred, not ninetyangle tolerance · drafting and CAD
Angular toleranceone tolerance — in arcminutes and in millimetres over a lengthstrength of materials · drafting and CAD
Second moment of areaone board: 16 times stiffer on edge than laid flatrolled steel · drafting and CAD
Linear mass of rolled sectionsa tonne by the table is shorter than a tonne from the millloads and actions · drafting and CAD
Distributed loada square metre becomes a metre of beam through the spacingadditive manufacturing · drafting and CAD
STL tessellation tolerancean arc the file stores as facetsdrawing layout · drafting and CAD
Linetype scalea dash that prints as a solid linedisplay precision · drafting and CAD
Unit precisiona hundred on screen, 99.9996 in fact
Drawing scalea number you assign, not measuredimensionless · drafting and CADScale in CADa scale that lives in the viewport, not in the partunit code · drafting and CADDrawing unitsa number that doesn’t know what it is measured inlength on paper · drafting and CADLineweighta thickness that shrinks with the sheetlength on paper · drafting and CADText heighta letter measured by its capitallength · drafting and CADThread pitchthe number of threads that decides whether the nut will go ondimensionless · drafting and CADTapera ratio that holds a drill without a keydimensionless · drafting and CADSlopethe rise along a length that makes a wedge hold itselflength · drafting and CADWeld legthe side you measure and the height that holdsclearance and interference · drafting and CADFittwo tolerance zones with the clearance living between themplane angle · drafting, CAD and surveyingGonan angle split into a hundred, not ninetyangle tolerance · drafting and CADAngular toleranceone tolerance — in arcminutes and in millimetres over a lengthstrength of materials · drafting and CADSecond moment of areaone board: 16 times stiffer on edge than laid flatrolled steel · drafting and CADLinear mass of rolled sectionsa tonne by the table is shorter than a tonne from the millloads and actions · drafting and CADDistributed loada square metre becomes a metre of beam through the spacingadditive manufacturing · drafting and CADSTL tessellation tolerancean arc the file stores as facetsdrawing layout · drafting and CADLinetype scalea dash that prints as a solid linedisplay precision · drafting and CADUnit precisiona hundred on screen, 99.9996 in fact04 · The prefix ribbon
From quetta to quecto
Q
10³⁰
quetta
R
10²⁷
ronna
Y
10²⁴
yotta
Z
10²¹
zetta
E
10¹⁸
exa
P
10¹⁵
peta
T
10¹²
tera
G
10⁹
giga
M
10⁶
mega
k
10³
kilo
h
10²
hecto
da
10¹
deca
d
10⁻¹
deci
c
10⁻²
centi
m
10⁻³
milli
µ
10⁻⁶
micro
n
10⁻⁹
nano
p
10⁻¹²
pico
f
10⁻¹⁵
femto
a
10⁻¹⁸
atto
z
10⁻²¹
zepto
y
10⁻²⁴
yocto
r
10⁻²⁷
ronto
q
10⁻³⁰
quecto
05 · Editors' choice
Where to begin
non-SI · American pneumatics
Pound per square inchthe unit you can hearnon-SI · rotational mechanics
Revolution per minutethe unit you read off a motor nameplate and check with a flashing lampnon-SI · a count of secondsUnix time and ISO 8601 notationa limit set by the width of the machine wordnon-SI · a zero point
Eraeleven eras on one scalenon-SI · analytical chemistry
Mole per litrea hot solution made up to the mark will cool stronger than the logbook saysnon-SI · solution chemistry
Potential of hydrogena scale with no unit, where every step is tenfold
Pound per square inchthe unit you can hearnon-SI · rotational mechanicsRevolution per minutethe unit you read off a motor nameplate and check with a flashing lampnon-SI · a count of secondsUnix time and ISO 8601 notationa limit set by the width of the machine wordnon-SI · a zero pointEraeleven eras on one scalenon-SI · analytical chemistryMole per litrea hot solution made up to the mark will cool stronger than the logbook saysnon-SI · solution chemistryPotential of hydrogena scale with no unit, where every step is tenfold06 · The history wing
An archive of knowledge that worked
Archive · 1780–1850
Caloric
A weightless fluid present in every body and the cause of thermal phenomena. A working formalism on which steam engines and the calorie were calculated.
Archive · 1795
The metric revolution
The metre as one forty-millionth of the meridian: a measure drawn from nature rather than from a king’s body.
Reform · 2019
SI on constants
The last physical prototype went to a museum: the kilogram is now defined through the Planck constant.
Archive · before 1918
Russian measures
Sazhen, arshin, pud, zolotnik: a system abolished by decree, still alive in texts and drawings.
07 · From quantum to cosmos
navigation by orders of magnitudePick a scale — get the units that live there
One ribbon stitches the Planck length to the radius of the observable Universe. The ticks are entrances — to where ångströms live, and to where parsecs do.
10⁻³⁵
Planck length
ℓP
10⁻¹⁵
proton
fm
10⁻¹⁰
atom
Å
10⁻⁶
cell
µm
10⁻³
grain of sand
mm
10⁰
human
m
10³
city
km
10¹¹
Earth orbit
au
10²⁶
observable Universe
Gpc
08 · Your language
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