Definitions

# Approximate conversion of units

Approximate conversion of units often needs to be done without calculator, computer, or sometimes even longhand. This article is an informal listing of some simple conversions between (and within) the imperial system, the U.S. customary system and the metric system/SI. When people say "a foot long" or "ten kilometres from here", they rarely mean "0.3048 m" or "6.21571 miles".

These are all rough approximations; for more accurate information, see Conversion of units.

Exact conversions can be performed in Google by typing the source and target units directly in the search box, using the keyword in.

For example; On entering
34 acres in hectares
in Google search box there is returned:
34 acres = 13.7593118 hectares.
The user should be conscious of the significant figures in the result generated.

## Length

### English units to metric units

1 point
= 352 µm
≈ 250 µm = ¼ mm
≈ 375 µm = mm
≈ 350 µm = mm
1 inch
= 25.4 mm = 2.54 cm
≈ mm = cm
≈ 25 mm = 2.5 cm
≈ 30 mm = 3 cm
2 in. ≈ 5 cm
4 in. ≈ 10 cm
6 in. ≈ 15 cm
8 in. ≈ 20 cm
10 in. ≈ 25 cm
1 foot
≡ yard = 0.3048 m
≈ 30 cm = 3 dm
≈ m = 3 dm
≈ ¼ m = 2.5 dm = 25 cm
1 yard
≡ 0.9144 m
≈ 0.9 m
≈ 1 m
1 fathom
= 6 foot = 1.8288 m
≈ 1.852 m
≈ 1.85 m
≈ 1.8 m
≈ 2 m
1 rod = 1 pole = 1 perch
= 198 in. = 5.0292 m
≈ 5 m
1 chain
= 22 yards = 4 rods = 20.1168 m
≈ 20 m
1 furlong
= 10 chain = 201.168 m
≈ 200 m
1 mile
= 8 furlong = 1.609344 km
≈ 1.609 km
≈ 1.61 km
≈ 1.6 km
≈ 1.5 km
≈ 2 km
3 miles ≈ 5 km
5 miles ≈ 8 km

### Metric units to English units

1 millimetre
= in.
≈ in. ≈ 0.992 mm
≈ in. ≈ 1.191 mm
≈ in. ≈ 0.794 mm
≈ in. ≈ 1.058 mm
≈ in. = 1.016 mm = 0.04 in.
1 centimetre
= in.
≈ in. ≈ 0.992 cm
≈ in. ≈ 1.032 cm
≈ in. ≈ 0.953 cm
≈ in. = 1.27 cm
≈ in. ≈ 1.005 cm
≈ in. ≈ 1.058 cm
≈ in. ≈ 0.847 cm
≈ in. = 1.016 cm = 0.4 in.
1 decimetre
= in.
≈ 4 in. = 1 hand
1 metre
≈ 1.1 yards
≈ 3 ft. 3 in.
≈ 3 ft. = 1 yard
1 kilometre
≈ 0.621 mile
≈ 3281 ft ≈ 1.00005 km
≈ 3280 ft ≈ 0.9997 km
≈ 5 furlong ≈ 1.006 km
≈ mile ≈ 1.073 km

### Geographical

Latitude distances anywhere and longitude distances at the equator
1° (degree) ≈ 100 km ≈ 62 statute miles = 60 nautical miles
1′ (minute) ≈ 2 km = 1 nautical mile
1″ (second) ≈ 30 m
1 cable = nautical mile
= 185.2 m
≈ 185 m
≈ 180 m
≈ 190 m
≈ 200 m
1 nautical mile (obsolete British definition)
= 6080 feet = 1.853184 km
≈ 1 equatorial minute = 1 meridian minute
≈ 1.853 km
≈ 1.852 km = 1 standard nautical mile
≈ 1.85 km
≈ 1.8 km
≈ 1.9 km
≈ 2 km

## Area

### English units to metric units

1 sq in
= 6.4516 cm²
≈ 6.5 cm²
1 sq ft
= 929.0304 cm²
≈ 930 cm²
≈ 9 dm²
≈ 0.1 m²
1 acre
= 4046.8564224 m²
≈ 4050 m² = 40.5 a
≈ 4000 m² = 40 a
≈ 5000 m² = 50 a = ½ ha
5 acres ≈ 2 ha
1 sq mi
≈ 2.59 km²
≈ 2.6 km²
≈ 2.5 km²
2 sq mi ≈ 5 km²

1 m²
≈ 10.76 sq. ft.
≈ 11 sq. ft.
≈ 10 sq. ft.
1 a
≈ 1076 sq. ft.
≈ 1100 sq. ft.
≈ 1000 sq. ft.
1 ha
≈ 107600 sq. ft.
≈ 110000 sq. ft.
≈ 100000 sq. ft.
≈ acre
1 km²
≈ 250 acres

## Volume

### Imperial to metric and U.S. customary units

1 imperial scruple
= drachm
≈ 1.184 ml
≈ 1.2 ml
≈ 1¼ ml
≈ 1 ml
1 imperial drachm
= imp. fl. oz
≈ 3.552 ml
≈ 3½ ml
1 imperial fluid ounce
= imp. pint
≈ 28.5 ml
≈ 28 ml
≈ 30 ml
≈ U.S. fl. oz.
≈ 1 U.S. fl. oz. - 1 ml
≈ 1 U.S. fl. oz.
1 imperial gill
= 5 imp. fl. oz.
≈ 142.065 ml
≈ 140 ml
≈ 150 ml
≈ 100 ml
1 imperial pint
= 20 imp. fl. oz.
≈ 570 ml
≈ 550 ml = 5½ dl
≈ 600 ml
≈ 500 ml = ½ l
≈ 1 pints (U.S. wet)
≈ 1 pint - 100 ml (U.S. wet)
≈ 1 pint 3 oz. (U.S. wet)
1 imperial quart
= ¼ imp. gal.
≈ 1.137 l
≈ 1.14 l
≈ 1.2 l
≈ 1 l
≈ 2½ pints (U.S. wet)
1 imperial gallon
= 8 imp. pints
≈ 4.55 l
≈ 4 l
≈ 1 gal. (U.S. wet)
≈ 154 fl. oz. (U.S. wet)
≈ 1.032 gal. (U.S. dry)
≈ 1 gal. (U.S. dry)
1 imperial peck
= 2 imp. gal.
≈ 9.092 l
≈ 9 l
≈ 10 l
1 imperial bushel
= 4 pecks
≈ 36.368 l
≈ 36 l
≈ 35 l
≈ 40 l
= 8 bushels
≈ 290.9 l
≈ 290 l
≈ 300 l
≈ 256 l
≈ 250 l the volume of ¼ t of water

### U.S. customary to metric and Imperial units

Wet
1 U.S. dram
= U.S. fl. oz.
≈ 3.697 ml
≈ 3.7 ml
≈ 3.75 ml = 3¾ ml
≈ 3½ ml
1 U.S. fluid ounce
≈ 29.574 ml
≈ 30 ml
≈ 25 ml
≈ 1 imp. fl. oz. + 1 ml
≈ 1 imp. fl. oz.
1 U.S. gill
= 4 U.S. fl. oz.
≈ 118.294 ml
≈ 120 ml
≈ 100 ml
≈ 150 ml
1 U.S. pint
= 16 U.S. fl. oz.
≈ 473.176 ml
≈ 475 ml = 4¾ dl
≈ 500 ml = ½ l
≈ imp. pints
1 U.S. quart
= U.S. gal.
≈ 0.946 l
≈ 1 l
1 U.S. gallon
≈ 3.785 l
≈ 3.8 l
≈ 3 l
≈ 4 l
≈ 5 l
≈ imp. gal.
1 oil barrel
= 42 U.S. gallon
≈ 158.987 l
≈ 159 l
≈ 160 l
≈ 35 imp. gal.

Dry
1 U.S. pint
≈ 550.61 ml
≈ 550 ml = 5½ dl
≈ 500 ml = ½ l
≈ 1 imp. pint
1 U.S. quart
= U.S. gal.
≈ 1.101 l
≈ 1.1 l
≈ 1 l
≈ 1 imp. quart
1 U.S. gallon
≈ 4.405 l
≈ 4.4 l
≈ 4.5 l
≈ 4 l
≈ 5 l
≈ 1 imp. gal.
1 U.S. peck
= 2 U.S. gal
≈ 8.810 l
≈ 8.8 l
≈ 9 l
≈ 10 l
1 U.S. bushel
= 4 U.S. peck
≈ 35.239 l
≈ 35 l
≈ 40 l
= 8 bushels
≈ 281.9 l
≈ 280 l
≈ 300 l
≈ 256 l
≈ 250 l the volume of ¼ t of water

### Metric to Imperial and U.S. customary units

 1 millilitre ≈ fl. oz. (imp. or U.S.) ≈ fl. oz. (imp. or U.S.) 1 centilitre ≈ fl. oz. (imp. or U.S.) 1 litre ≈ 1 pints (imp.) ≈ 2 pints (wet U.S) ≈ 1.05 quarts (wet U.S) ≈ gal. (wet U.S.)

### Kitchen

 1 teaspoon ≈ 5 ml 1 tablespoon ≈ 15 ml 1 cup ≈ 225 ml ≈ 240 ml ≈ 250 ml = ¼ l

## Mass and weight

### Avoirdupois to metric units

 1 grain = 64.79891 mg ≈ 65 mg ≈ 50 mg 1 drachm = ounce ≈ 1.772 g ≈ 1 g ≈ 1 g ≈ 2 g 1 ounce = pound ≈ 28.35 g ≈ 28.5 g ≈ g ≈ 30 g ≈ 25 g 1 pound = 7000 grains ≈ 453.592 g ≈ 450 g ≈ 500 g

Long
1 stone
= 14 pounds
≈ 6.35 kg
≈ 6 kg
≈ 5 kg
1 quarter
= 28 pounds
≈ 12.701 kg
≈ 12.5 kg
1 hundredweight
= 112 pounds
≈ 50.802 kg
≈ 50 kg
1 ton
= 2240 pounds
≈ 1.016 t
≈ 1 t
= 1.12 short tons
≈ 1 short ton

Short
1 quarter
= 25 pounds
≈ 11.34 kg
≈ 11 kg
≈ 10 kg
1 hundredweight
= 100 pounds
≈ 45.359 kg
≈ 45 kg
≈ 50 kg
1 ton
= 2000 pounds
≈ 0.907 t
≈ 0.9 t
≈ 1 t
≈ 0.893 long tons
≈ 0.9 long tons
≈ 1 long ton

### Metric units to Avoirdupois

 1 carat = 200 mg ≈ 3 grains 1 gram ≈ 15.5 grains ≈ 16 grains ≈ 15 grains ≈ oz. ≈ oz. 1 kilogram ≈ 2.2 lb. ≈ 2 lb. 1 tonne ≈ 1 long ton ≈ 1.1 short ton ≈ 1 short ton

### Troy to metric units

 1 grain = 64.79891 mg ≈ 65 mg ≈ 50 mg 1 pennyweight = 24 grains ≈ 1.555 g ≈ 1.5 g 1 ounce = 20 pennyweight ≈ 31.103 g ≈ kg ≈ 30 g ≈ kg ≈ 25 g '''1 pound = 12 ounces ≈ 373.242 g ≈ 375 g ≈ 350 g ≈ 400 g ≈ 500 g

## Velocity

 1 km/h ≈ 0.3 m/s ≈ 1 foot per second (ft/s) 2 km/h ≈ ½ m/s ≈ 1 knot 3 km/h ≈ 1 m/s ≈ 2 miles per hour (mph)

## Force

 3 N ≈ 20 poundal 5 N ≈ 1 pound-force (lbf)

## Pressure

 1 bar = 1000 hPa ≈ 1 atm ≈ 15 psi 4 mbar = 4 hPa ≈ 3 torr = 3 mmHg 100 mbar = 10 kPa ≈ 3 inch mercury

## Energy

 4 J ≈ 1 calorie 1 kJ ≈ 1 British thermal unit

## Power

 3 kW ≈ 4 horsepower

## Temperature

Fahrenheit to Celsius -- subtract 32, divide by 1.8
Examples:

• 212 - 32 = 180; 180 /1.8 = 100 Water Boils in Degrees Celsius
• 98.6 - 32 = 66.6; 66.6 / 1.8 = 37 Normal Human Body Temperature in Degrees Celsius
• 68 - 32 = 36; 36 / 1.8 = 20 Comfortable temperature in Degrees Celsius
• 32 - 32 = 0; 0/1.8 = 0 Water Freezes in Degrees Celsius
• -40 - 32 = -72; -72 /1.8 = -40 Only Temperature the Same in Celsius and Fahrenheit

Celsius to Fahrenheit -- multiply by 1.8, add 32
Examples:

• 100 x 1.8 = 180; 180 + 32 = 212 Water Boils in Degrees Fahrenheit
• 37 x 1.8 = 66.6; 66.6 + 32 = 98.6 Normal Human Body Temperature in Degrees Fahrenheit
• 20 * 1.8 = 36; 36 + 32 = 68 Comfortable temperature in Degrees Fahrenheit
• 0 x 1.8 = 0; 0 + 32 = 32 Water Freezes in Degrees Fahrenheit
• -40 x 1.8 = -72; -72 + 32 = -40 Only Temperature the Same in Celsius and Fahrenheit

## References

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