Prefixes

Units can be used as such or in multiples or fractions of ten:

PREFIX		POWER OF TEN
T	tera	1012
G	giga	109
M	mega	106
k	kilo	103
h	hecto	102
da	deca	101
d	deci	10-1
c	centi	10-2
m	milli	10-3
m	micro	10-6
n	nano	10-9
P	pico	10-12
f	femto	10-15
a	atto	10-18

1 m = 100 cm = 1000 mm
1 m² = 10 000 cm² = 10⁶ mm²
1 m³ = 10⁶ cm³ = 10⁹ mm³
1 Mg m^-3 = 10³ kg m^-3 = 1 g cm^-3
1 kPa = 10 mbar
1 joule = 0.2388 cal
1 watt = 1 J s-1 = 0.8598 kcal h^-1
1 W m^-2 = 0.8598 kcal m^-2 h^-1
1 W m^-2 = 1.433 × 10^-3 cal cm^-2 min^-1
1 Hp = 745.7 W
1 W = 0.001431 Hp
Water flow (m³ s^-1) = 0.55 × Pump power (W)/Pressure (kPa)
Water flow (litre s^-1) = 5.43 × Pump power (kilowatts)/pressure (bars)

Brake Horsepower is the horsepower for an electric motor. Do not use for fuel-powered engines.

Conversion factors

Temperature

Standard unit: degree Celsius (°C)

degree Fahrenheit (°F)	°C = (°F-32) 5/9
kelvin(s) (K)	K = °C +273.15

Pressure (air pressure, vapour pressure)

Standard unit: kilopascal (kPa)

millibar (mbar)	1 mbar = 0.1 kPa
Bar	1 bar = 100 kPa
centimetre of water (cm)	1 cm of water = 0.09807 kPa
millimetre of mercury (mm Hg)	1 mm hg = 0.1333 kPa
atmosphere (atm)	1 atm =101.325 kPa
pound per square inch (psi)	1 psi = 6.896 kPa

Wind speed

Standard unit: metre per second (m s^-1)

kilometre per day (km day-1)	1 km day-1 = 0.01157 m s-1
nautical mile/hour (knot)	1 knot = 0.5144 m s-1
foot per second (ft s-1)	1 ft s-1 = 0.3048 m s-1

Radiation

Standard unit: megajoule per square metre and per day (MJ m² day^-1) or as equivalent evaporation in mm per day (mm day^-1)

equivalent evaporation (mm/day)	1 mm day-1 = 2.45 MJ m-2 day-1
joule per cm2 per day (J cm-2 day-1)	1 J cm-2 day-1 = 0.01 MJ m-2 day-1
calorie per cm2 per day (cal cm-2 day-1)	1 cal = 4.1868 J = 4.1868 10-6 MJ
	1 cal cm-2 day-1 = 4.1868 10-2 MJ
	m-2 day-1
watt per m2 (W m-2)	1 W = 1 J s-1
	1 W m-2 = 0.0864 MJ m-2 day-1

Physical properties

Properties of Water

T	rw	l
°C	Mg m-3	kJ mol-1
0	0.99987	45.0
4	1.00000	44.8
10	0.99973	44.6
20	0.99823	44.1
30	0.99568	43.7
40	0.99225	43.4

T = temperature, r_w = density of water and l = latent heat of vaporization

Properties of gases at P_b = 101.3 kPa barometric pressure

T	r
°C	mol m-3
0	44.6
5	43.8
10	43.0
15	42.3
20	41.6
25	40.9
30	40.2
35	39.5
40	38.9

T= temperature and r = density

Black body emittance (W m^-2) as a function of subzero temperature (°C)

°C	0.0	-0.1	-0.2	-0.3	-0.4	-0.5	-0.6	-0.7	-0.8	-0.9
-14	256	255	255	255	254	254	253	253	253	252
-13	260	259	259	258	258	258	257	257	257	256
-12	264	263	263	262	262	262	261	261	260	260
-11	268	267	267	267	266	266	265	265	265	264
-10	272	271	271	271	270	270	269	269	269	268
-9	276	276	275	275	274	274	274	273	273	272
-8	280	280	279	279	279	278	278	277	277	276
-7	284	284	284	283	283	282	282	282	281	281
-6	289	288	288	287	287	287	286	286	285	285
-5	293	293	292	292	291	291	291	290	290	289
-4	298	297	297	296	296	295	295	294	294	294
-3	302	302	301	301	300	300	299	299	298	298
-2	306	306	306	305	305	304	304	303	303	302
-1	311	311	310	310	309	309	308	308	307	307
0	316	315	315	314	314	313	313	312	312	311