            + Contact NASA              + Home               Print this page   ### Appendix E - Units of Measure and Conversion Factors | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z |

USER'S GUIDE

This section presents definitions, physical constants and conversion factors that are used in the text and may be useful as reference data. Scroll down through the list or use the alphabetical links below to go directly to the section where your word or symbol is located.

### A #### ATMOSPHERE (atm):

The pressure exerted by 76 cm mercury with a density of 13.5951 gm/cm3 at 1g (the standard barometric pressure at sea level).

1 atm        = 325 x 106 dynes/cm 2

1 atm        = 1033.2 gm/cm 2

1 atm        = 760 mm Hg

1 atm        = 14.696 psi

1 atm        = 101.329 kPa (kilo Pascals)

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### B #### BRITISH THERMAL UNIT (Btu):

1 Btu        = 1.0559 x 1010 ergs

1 Btu        = 1055.9 joules

1 Btu        = 251.995 gm-cal

1 Btu        = 778.77 ft-lbs

1 Btu        = 0.25199 kcal

1 Btu/hr        = 0.1667 Btu/min

1 Btu/hr        = 0.04199 kcal/min

1 Btu/hr        = 0.2932 watt

1 Btu/min        = 0.25199 kcal\min

1 Btu/min        = 0.23599 hp

1 Btu/min        = 17.595 watts

1 Btu/ft2, hr        = 2.7125 kcal/m2 hr

Btu/hr to joules:

1 Btu/hr  = 1.05435 x 103 joule/hr

800 Btu/hr x 1054.35 = 843480 joule/hr

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### C #### CANDELA (cd):

1 cd                    = 1.018 candle

#### CANDLE (c):

The unit of luminous intensity.

#### CENTIMETER (cm):

1 cm        = 0.03280 ft

1 cm        = 0.3937 in

1 cm        = 0.01 m

1 cm        = 10mm

1 cm        = 1x104m (micron)

#### CENTIMETER-CANDLE (phot):

1 phot                 = 1 x 104 lux

#### CENTIMETERS PER SECOND PER SECOND:

1 cm/sec2            = 0.0328 ft/sec2

#### CLO (clo):

The unit of insulation resistance for clothing.

1 clo    = 0.18°C m2hr/kcal

1 clo    = 0.88°F ft2hr/Btu

#### CUBIC CENTIMETER (cc or cm3):

1 CC    = 3.531 x 10-5 ft3

1 CC    = 0.061023 in3

1 CC    = 1 x 10-6 m3

1 CC    = 1000 mm3

1 CC    = 2.6417 x 10-4 gal (US fluid)

1 CC    = 0.0338 oz (US fluid)

1 CC    = 2.113 x 10-3 pint (US fluid)

1 cc/sec    = 0.0021186 ft3/min

#### CUBIC FOOT

1 ft3    = 1728 in3

1 ft3    = 28.32 liters

1 ft3    = 0.02832 m3

1 ft3/min    = 472.0 cc/sec

1 ft3/min    = 0.4720 liter/sec

1 ft3/min    = 62.43 lbs H2O/min

1 ft3/sec    = 1699.3 liters/min

#### CUBIC INCH:

1 in3    = 5.787 x 10-4 ft3

1 in3    = 1.639 x 102 liter

1 in3    = 1.639 x 10-5 m3

#### CUBIC METER:

1 m3    = 35.3144 ft3

1 m3    = 6.1023 x 104 in3

1 m3    = 999.973 liters

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### D #### DECIBEL (db):

Used for comparing power levels, acoustical or electrical.  (See also Sound Pressure Level).

1 db    = 10 log10 P/PO

where P is the power to be compared to a reference power PO

1 db    = 1 bel is equal to an increase in power (P) by a factor of 10

#### DEGREE (ANGULAR) (deg):

1 deg    = 60 minutes

1 deg    = 3600 seconds

1 deg    = 1.7453 X 10-2 steradian --- note, this is changed from the original version that contains an error

60° x π/180 = 1.0472  = 1 rad

°C    = 5/9 * (°F - 32)

#### DEGREES FAHRENHEIT (°F):

°F    = (9/5 * °C) + 32

#### DEGREES PER SECOND:

1 deg/sec    = 0.1667 rpm

#### DYNE (dyne):

1 dyne    = 1.0197 x 10-6 kg

1 dyne    = 2.2481 x 10-6 lb

1 dyne-cm    = 1 erg

#### DYNE PER SQUARE CENTIMETER

1 dyne/cm2    = 9.8692 x 10-7 atm

1 dyne/cm2    = 0.0010197 gm/cm2

1 dyne/cm2    = 4.0148 x 10-4 in H2O

1 dyne/cm2    = 7.5006 x 10-4 mm Hg

1 dyne/cm2    = 1.4504 x 10-5 psi

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### E #### ERG (erg):

1 erg    = 9.4805 x 10-11 Btu

1 erg    = 7.3756 x 10-8 ft-lb

1 erg    = 2.3889 x 10-11 kcal

1 erg    = 8.8510 x 10-7 lb-in

1 erg    = 1 dyne-cm

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### F #### FAHRENHEIT (°F):

(See Degrees Fahrenheit).

#### FOOT (ft):

1 ft    = 30.48 cm

1 ft    = 12 in

1 ft    = 0.3048 m

#### FOOT-CANDLE (fc):

1 ft-c    = 1 lumen/ft2

1 ft-c    = 10.764 lumen/m2

1 ft-c    = 10.75 lux

#### FOOT-LAMBERT (ft-L):

1 ft-L    = 1.0764 millilamberts

1 ft-L    = 0.32 decibels with respect to 1 mL

#### FOOT PER MINUTE

1 ft/min    = 0.3048 m/min

1 ft/min    = 0.005080 m/sec

1 ft/min    = 0.011364 mph

#### FOOT PER SECOND:

1 ft/sec    = 1.0973 km/hr

1 ft/sec    = 0.5921 knot

1 ft/sec    = 0.6818 mph

#### FOOT-POUND (ft-lb):

1 ft-lb    = 0.001285 Btu

1 ft-lb    = 1.3558 x 107 ergs

1 ft-lb    = 3.2389 x 10-4 kcal

1 ft-lb/min    = 3.0303 x 10-5 hp

1 ft-lb/min    = 0.01667 ft-lb/sec

1 ft-lb/min    = 0.022597 watt

1 ft-lb/sec    = 0.001818 hp

1 ft-lb/sec    = 0.01943 kcal/min

1 ft-lb/sec    = 1.3558 watts

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### G #### G (g):

The acceleration of gravity (also the acceleration of a vehicle).

1g = 9.81 m/s2

1 ft/sec    = 1.0973 km/hr

1 ft/sec    = 0.5921 knot

1 ft/sec    = 0.6818 mph

#### GRAM (gm):

1 gm    = 0.001 kg

1 gm    = 1000 mg

1 gm    = 0.03527 oz

1 gm    = 0.0022046 lb

1 gm/cm3    = 62.428 lbs/ft3

1 gm/hr    = 0.540 lb/day

1 gm/hr    = 0.0003757 lb/min

1 gm/liter    = 0.062427 lb/ft3

1 gm/cm2    = 9.6784 x 10-4 atm

1 gm/cm2     = 980.665 dynes/cm2

1 gm/cm2     = 0.9356 mm Hg

1 gm/cm2     = 0.014223 psi

1 gm/m2/hr    = 2.78 x 10-5 gm/cm2/sec

1 gm/m2/hr    = 0.7448 lb/ft2/hr

#### GRAM-CALORIE (gm-cal):

1 gm-cal    = 30874 ft-lbs

1 gm-cal    = 0.001 kcal

#### GRAY (Gy):

The International System of Units (SI) unit for the amount of ionizing radiation energy absorbed by tissue.

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### H #### HORSEPOWER (hp):

1 hp    = 3.300 x 104 ft-lbs/min

1 hp    = 550 ft-lbs/sec

1 hp    = 10.688 kcal/min

1 hp    = 745.7 watts

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### I #### INCH (in):

1 in    = 2.540 cm

1 in    = 0.0833 ft

1 in    = 25.40 mm

#### INCH OF WATER (in H2O):

1 in H2O  (at 4°C)    = 0.002458 atm

1 in H2O  (at 4°C)    = 2490.82 dynes/cm2

1 in H2O  (at 4°C)    = 0.0361 psi

1 in H2O (at 4°C)    = 1.868 mm Hg

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### J #### JOULE (joule):

1 joule               = 1 watt-sec

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### K #### KILOGRAM (kg):

1 kg    = 1000 gm

1 kg    = 2.205 lb

1 kg    = 35.28 oz

#### KILOGRAM-CALORIE (kcal or large Calorie):

1 kcal    = 3.9683 Btu

1 kcal    = 4.186 x 1010 ergs

1 kcal    = 1000 gm-cal

1 kcal    = 3087 ft-lbs

1 kcal/hr    = 0.0661 Btu/min

1 kcal/hr    = 0.857 ft-lbs/sec

1 kcal/hr    = 0.1667 kcal/min

1 kcal/hr    = 1.161 watts

1 kcal/m2hr    = 0.3687 Btu/ft2hr

1 kcal/min    = 3.9685 Btu/min

1 kcal/min    = 51.457 ft-lbs/sec

1 kcal/min    = 0.093557 hp

1 kcal/min    = 69.767 watts

#### KILOGRAM-CENTIMETER SQUARED:

1 kg-cm2    = 0.3417 lb-in2

#### KILOGRAM-METER PER SECOND:

1 kg-m/sec    = 7.2330 ft-lb/sec

1 kg-m/sec    = 9.80665 watts

#### KILOMETER (km):

1 km    = 105 cm

1 km    = 3281 ft

1 km    = 103 meters, m

1 km    = 0.6214 statute miles, mi

1 km    = 0.54 nautical miles, nm

#### KILOPASCAL:

1kPa    = 6.895 psi

1kPa    = 4.754 x 105 dynes/cm2

1 psi    = 0.145 kPa

#### KILOMETERS PER HOUR:

1 km/hr    = 0.9113 ft/sec

1 km/hr    = 0.5396 knot

1 km/hr    = 0.6214 mph

#### KNOT (nautical mile per hour):

1 knot    = 1.689 ft/sec

1 knot    = 1.853 km/hr

1 knot    = 1.1516 mph

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### L #### LAMBERT (L):  Unit of surface brightness.

1L    = 0.3183 c/cm2

1L    = 2.0536 c/in2

1L    = 1 lumen/cm2

#### LITER (l):

1 liter    = 0.03531 ft3

1 liter    = 61.02 in3

1 liter    = 1000 ml

1 liter/min    = 5.886 x 10-4 ft3/sec

1 liter/sec    = 2.12 ft3/min

#### LUMEN (lumen):

1 lumen    = 0.001496 watt

1 lumen    = 0.07958 spherical candle power

1 lumen/ft2    = 1 ft-c

1 lumen/ft2    = 10.764 lumen/m2

#### LUMENS PER SQ. METER TO FT CANDLES:

1 lumen/m2    = 0.0929 ft. candle

#### LUX:

1 lux    = 0.093 ft-c (see meter-candle)

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### M 1m    = 100 cm

1m    = 3.281 ft

1m    = 39.37 in

#### METER-CANDLE (lux):

1 lux    = 1 lumen/m2

1 lux    = 0.092903 ft-c

#### METER PER SECOND (m/sec):

1 m/sec    = 3.281 ft/sec

1 m/sec    = 3.600 km/hr

1 m/sec    = 2.2369 mph

#### MICRON (μ or mu):

A unit of length equal to one-millionth of a meter or one-thousandth of a millimeter, usually called micrometer.

1 μ    = 10-6 meter

1 μ    = 3.937 x 10-5 in

1 μ    = 0.001 mm

#### MIL (mil):

1 mil    = 0.001 in

1 mil    = 0.0254 mm

1 mil    = 25.40μ (microns)

#### MILES (statute) (mi):

1 mi    = 1,609 x 105 cm

1 mi    = 5,280 ft

1 mi    = 1.609 km

#### MILES PER HOUR (mph)

1 mph    = 88 ft/min

1 mph    = 1.4667 ft/sec

1 mph    = 1.6093 km/hr

1 mph    = 0.8684 knot

#### MILLIGRAM (mg):

1 mg    = 0.001 gm

1 mg    = 3.5274 x 10-5 oz

1 mg    = 2.2046 x 10-6 lb

1 mg/m3    = 6.243 x 10-4 lb/ft3

#### MILLILAMBERT (ml):

(perfectly diffused light)

1 mL    = 0.929 lumen/ft2

#### MILLILITER (ml):

1 ml    = 1.000028 cc

1 ml    = 0.061025 in3

1 ml    = 0.001 liter

1 ml    = 0.0338 oz (US fluid)

#### MILLILITERS PER HOUR:

1 ml/hr    = 0.06102 in3/hr

#### MILLIMETER(mm):

1mm    = 0.10 cm

1mm    = 0.03937 in

1mm    = 1000 μ

#### MILLIMETER OF MERCURY (mm Hg):

1mm Hg (at 0°C)    = 0.0013158 atm

1mm Hg (at 0°C)    = 1333.22 dyne/cm2

1mm Hg (at 0°C)    = 1.3595 gm/cm2

1mm Hg (at 0°C)    = 0.019337 psi

1mm Hg (at 0°C)    = 0.535 in H2O

1mm Hg (at 0°C)    = 0.1333 kPa

#### MILLISECONDS (msec):

1 msec              = 0.001 sec

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### N #### NAUTICAL MILES (nm):

1 nm    = 0.87 statute miles

1 nm    = 1.85 kilometers

#### NEWTONS TO POUNDS:

1 N           = 0.22507 lbf

#### NEWTON CENTIMETERS TO INCH OUNCES:

1 N-cm     = 1/.706 in oz

70N-cm x 1/.706  = 99.15    = 100 in oz

#### NEWTON METERS TO FOOT POUNDS:

1Nm    = 1/1.356 ft lb

15Nm x 1/1.356    = 11.06    = 11 ft lb

#### NEWTON METERS TO INCH POUNDS:

1 Nm    = 1/.11298 in lb

4 Nm x 1/.11298      = 35.4      = 3 5 in lb

#### NIT:

Unit of luminance equal to the luminance provided by one candle of radiant flux emitted per square meter of surface - candela per square meter (Cd m2).

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### O #### OUNCE (oz):

1 oz     = 28.3495 gm

1 oz     = 0.0625 lb

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### P #### PASCALS (Pa)

Pa    = 4.75389 dynes/cm2

Pa    = 6.895 x 10-3 psi

#### PARTS PER MILLION (ppm).

1 ppm    = 1.0 mg/liter of H2O

1 ppm    = 8.345 lbs/million gallons

#### PHON (phon):

1 phon unit    = SPL of a 1000 cycle/sec tone

#### PHOT:

(See Centimeter Candle)

#### Physical Constants:

##### Acceleration of gravity (g)

= 32.17 ft/sec2= 980.6 cm/sec2

= 6.0221367 x 1023 molecules/gram-mole

##### Density of air at 0°C and 760 mm Hg

= 0.0012929 grams/cm3(0.0807 lb/ft3)

##### Density of water at 0°C

= .099984 grams/cm3

##### Heat of fusion of water at 1.0 atm

= 79.7 calories/gram = 144 Btu/pound

##### Heat of vaporization of water at 1.0 atm

= 540 calories/gram = 970 Btu/pound

= 2.71828183

= 3.14159265

##### Specific heat of air

= Cp = 0.238 cal/gram (°C)

##### Velocity of light (c)

= 2.99792458 x 1010 cm/sec

##### Velocity of sound in dry air at 0°C, 1 atm

= 33,136 cm/sec = 1,089 feet/sec

#### POISE: Unit of viscosity.

1 poise    = 1 dyne/sec, cm2

1 poise    = 1 gm/cm, sec

1 poise    = 0.067196 lb/ft, sec

#### POUND (lb):

1 lb    = 453.5924 gm

1 lb    = 0.45359 kg

1 lb    = 16 oz

1 lb    = 4.448 N

1 lb/day    = 18.89 gm/hr

1 lb/hr    = 0.7559 gm/min

1 lb/hr    = 10.886 kg/day

#### POUND-INCH (lb-in):

1 lb-in    = 1.1298 x 106 dyne/cm

#### POUND-INCH SQUARED:

Unit of moment of inertia

1 lb-in2    = 2.9264 kg-cm2

#### POUND OF WATER PER MINUTE (lb H2O/min):

1 lb H2O/min    = 0.01603 ft3/min

1 lb H2O/min    = 2.670 x 10-4 ft3/sec

#### POUND PER CUBIC FOOT (lb/ft3):

1 lb/ ft3    = 0.01602 gm/ cm3

#### POUNDS PER SQUARE INCH (psi):

1 psi    = 0.06805 atm

1 psi    = 6.8947 x 104 dyne/cm2

1 psi    = 70.307 gm/cm2

1 psi    = 51.715 mmHg

1 psi    = 27.7 in H2O

1 psi    = 145.03 Pa

#### POUNDS PER SQUARE INCH ABSOLUTE (psia):

Absolute pressure, where 0 psia = vacuum

1 psia    = 0.1449 kpascals

#### POUND WEIGHT (1 wt):

1 lb wt    = 4.4482 x 105 dynes

1 lb wt    = 453.59 gm wt

1 lb wt    = 16 oz

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### R 1 radian    = ½π circumference revolution (0.15915)

#### REVOLUTIONS PER MINUTE (rpm):

1 rpm    = 6 deg/sec

#### ROENTGEN (r):

1 r    = ionization by x-rays or gamma-rays producing 1 electrostatic unit of charge in 1 cm3 of air (STP)

1 r    = 83.0 ergs/gm

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### S #### SIEVERT (Sv):

Sv is the International System of Units (SI) unit for ionizing radiation dose equivalent. (Refer to Figure 5.7.2.1.3.1-1 for definition of Q values)

1 Sv    = 100 rem = (Gy) (Q)

#### SOUND PRESSURE LEVEL (SPL):

SPL is sound pressure related logarithmically to a reference level of pressure (Po), which by convention is 0.0002 dynes/cm2. The defining equation is:

SPL     = 20 log10 P/PO in decibels

#### SQUARE CENTIMETER (cm2):

1 cm2    = 1.076 x 10-3 ft2

1 cm2    = 0.1550 in2

1 cm2    = 100 mm2

#### SQUARE FOOT (ft2):

1 ft2    = 929.0304 cm2

1 ft2      = 144 in2

#### SQUARE INCH (in2):

1 in2    = 6.4516 cm2

1 in2    = 0.006944 ft2

1 in2    = 645.1626 mm2

#### SQUARE MILLIMETER (mm2):

1 mm2    = 0.01 cm2

1 mm2    = 0.001550 in2     + Web Accessibility and Policy Notices at JSC + Human Health & Performance Directorate + Johnson Space Center + NASA  Curator: HHPIT AppDev Team Content Manager: Jurine Adolf NASA Official: Pamela Bieri Last Updated: 08/27/2020 + Contact Us   