How many cubic centimeters in a liter? How many feet in a kilometer? What about gallons per minute and liters per second?

*Every* single engineer needs to convert units. What may change is *how* he does it.

- Find an online converter / ask Google;
- Use a desktop application, such as convert;
- Or do it on-the-fly with Emacs!

Now, you may ask:

“But why on earth would I ever consider Emacs to convert my units?”

Because Emacs has an amazing hidden gem inside it: Calc. Fear not, there is no need to learn yet another tool only to convert some units; I’ve package everything needed in a little .el file.

Once this is installed, you can ask Emacs, *on-the-fly*, to convert some units. Here is an example:

Old value and unit (type C-z for unit list) :

`100oz`

RET

to unit (type C-z for unit list) : g

`g`

RET

100oz converted to g = 2834.9523125 g

Pretty nice, isn’t it?

But this is far from it. What’s really handy is how you can input usual prefixes, such as k (kilo), m (milli), y (yocto)… without any special care.

Old value and unit (type C-z for unit list) :

`kg`

RET

to unit (type C-z for unit list) :

`g`

RET

kg converted to g = 1000 g

Tada!

What if you need units not yet defined in Calc? Simply add your own!

Here are some units I’ve added to be more helpful in a HVAC context:

;;; Add some custom units often used in HVAC (eval-after-load "calc-units" '(progn (setq math-additional-units '((gpm "gal / min" "Gallons per minute") (ls "l / s" "Liters per second") (cfm "ft^3 / min" "Cubic feet per minute")) math-units-table nil)))

Finally, to make sure you take Emacs and Calc seriously, here is the unit list (obtained with M-x `calc-view-units-table`

):

Calculator Units Table: (All definitions are exact unless marked with an asterisk (*).) Unit Type Definition Description gpm U gal / min Gallons per minute ls U l / s Liters per second cfm U ft^3 / min Cubic feet per minute m m Meter (base unit) in 2.54 cm Inch ft 12 in Foot yd 3 ft Yard mi 5280 ft Mile au 149597870691 m (*) Astronomical Unit lyr c yr Light Year pc 3.0856775854 10^16 m (*) Parsec nmi 1852 m Nautical Mile fath 6 ft Fathom fur 660 ft Furlong mu 1 um Micron mil (1/1000) in Mil point (1/72) in Point (1/72 inch) Ang 10^-10 m Angstrom mfi mi + ft + in Miles + feet + inches texpt (100/7227) in Point (TeX conventions) texpc 12 texpt Pica texbp point Big point (TeX conventions) texdd (1238/1157) texpt Didot point texcc 12 texdd Cicero texsp (1/65536) texpt Scaled TeX point hect 10000 m^2 Hectare a 100 m^2 Are acre (1/640) mi^2 Acre b 10^-28 m^2 Barn L 10^-3 m^3 Liter l L Liter gal 4 qt US Gallon qt 2 pt Quart pt 2 cup Pint cup 8 ozfl Cup ozfl 2 tbsp Fluid Ounce floz 2 tbsp Fluid Ounce tbsp 3 tsp Tablespoon tsp 4.92892159375 ml Teaspoon vol tsp+tbsp+ozfl+cup+pt+qt+gal Gallons + ... + teaspoons galC galUK Canadian Gallon galUK 4.54609 L UK Gallon s s Second (base unit) sec s Second min 60 s Minute hr 60 min Hour day 24 hr Day wk 7 day Week hms wk + day + hr + min + s Hours, minutes, seconds yr 365.25 day Year (Julian) Hz 1 / s Hertz mph mi / hr Miles per hour kph km / hr Kilometers per hour knot nmi / hr Knot c 299792458 m / s Speed of light ga 9.80665 m / s^2 "g" acceleration g g Gram (base unit) lb 16 oz Pound (mass) oz 28.349523125 g Ounce (mass) ton 2000 lb Ton tpo ton + lb + oz Tons + pounds + ounces (mass) t 1000 kg Metric ton tonUK 1016.0469088 kg UK ton lbt 12 ozt Troy pound ozt 31.10347680 g Troy ounce ct 0.2 g Carat u 1.660538782 10^-27 kg (*) Unified atomic mass N m kg / s^2 Newton dyn 10^-5 N Dyne gf ga g Gram (force) lbf ga lb Pound (force) kip 1000 lbf Kilopound (force) pdl 0.138254954376 N Poundal J N m Joule erg 10^-7 J Erg cal 4.1868 J International Table Calorie calth 4.184 J Thermochemical Calorie Cal 1000 cal Large Calorie Btu 1055.05585262 J International Table Btu eV ech V Electron volt ev eV Electron volt therm 105506000 J EEC therm invcm h c / cm Energy in inverse centimeters Kayser invcm Kayser (inverse centimeter energy) men 100 / invcm Inverse energy in meters Hzen h Hz Energy in Hertz Ken k K Energy in Kelvins Wh W hr Watt hour Ws W s Watt second W J / s Watt hp 550 ft lbf / s Horsepower hpm 75 m kgf / s Metric Horsepower K K K Degree Kelvin (base unit) dK K K Degree Kelvin degK K K Degree Kelvin dC C K Degree Celsius degC C K Degree Celsius dF F (5/9) K Degree Fahrenheit degF F (5/9) K Degree Fahrenheit Pa N / m^2 Pascal bar 10^5 Pa Bar atm 101325 Pa Standard atmosphere Torr (1/760) atm Torr mHg 1000 Torr Meter of mercury inHg 25.4 mmHg Inch of mercury inH2O 2.490889 10^2 Pa (*) Inch of water psi lbf / in^2 Pounds per square inch P (1/10) Pa s Poise St 10^-4 m^2 / s Stokes A A Ampere (base unit) C A s Coulomb Fdy ech Nav Faraday e ech Elementary charge ech 1.602176487 10^-19 C (*) Elementary charge V W / A Volt ohm V / A Ohm mho A / V Mho S A / V Siemens F C / V Farad H Wb / A Henry T Wb / m^2 Tesla Gs 10^-4 T Gauss Wb V s Weber cd cd Candela (base unit) sb 10000 cd / m^2 Stilb lm cd sr Lumen lx lm / m^2 Lux ph 10000 lx Phot fc lm / ft^2 Footcandle lam 10000 lm / m^2 Lambert flam (1 / pi) cd / ft^2 Footlambert Bq 1 / s Becquerel Ci 37 10^9 Bq Curie Gy J / kg Gray Sv Gy Sievert R 258 10^-6 C / kg Roentgen rd (1/100) Gy Rad rem rd Rem mol mol Mole (base unit) rad rad Radian (base unit) circ 2 pi rad Full circle rev circ Full revolution deg circ / 360 Degree arcmin deg / 60 Arc minute arcsec arcmin / 60 Arc second grad circ / 400 Grade rpm rev / min Revolutions per minute sr sr Steradian (base unit) h 6.62606896 10^-34 J s (*) Planck's constant hbar h / 2 pi Planck's constant mu0 4 pi 10^-7 H / m Permeability of vacuum eps0 1 / mu0 c^2 Permittivity of vacuum G 6.67428 10^-11 m^3/(kg s^2) (*) Gravitational constant Nav 6.02214179 10^23 / mol (*) Avogadro's constant me 9.10938215 10^-31 kg (*) Electron rest mass mp 1.672621637 10^-27 kg (*) Proton rest mass mn 1.674927211 10^-27 kg (*) Neutron rest mass mmu 1.88353130 10^-28 kg (*) Muon rest mass Ryd 10973731.568527 /m (*) Rydberg's constant k 1.3806504 10^-23 J/K (*) Boltzmann's constant alpha 7.2973525376 10^-3 (*) Fine structure constant muB 927.400915 10^-26 J/T (*) Bohr magneton muN 5.05078324 10^-27 J/T (*) Nuclear magneton mue -928.476377 10^-26 J/T (*) Electron magnetic moment mup 1.410606662 10^-26 J/T (*) Proton magnetic moment R0 8.314472 J/(mol K) (*) Molar gas constant V0 22.710981 10^-3 m^3/mol (*) Standard volume of ideal gas Unit Prefix Table: Y 10^24 Yotta Z 10^21 Zetta E 10^18 Exa P 10^15 Peta T 10^12 Tera G 10^9 Giga M 10^6 Mega k K 10^3 Kilo h H 10^2 Hecto D 10^1 Deka d 10^-1 Deci c 10^-2 Centi m 10^-3 Milli u 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