Units and conversions

Write a number and a unit and Babbage knows what it is. Put in, to or as and another unit after it and you get a conversion. Units combine in sums and products the way you would expect, and speeds, prices per unit and fuel economy are units too.

Every conversion factor is an exact fraction, so 1 mile in feet is exactly 5,280 ft and 3 kWh in MJ is exactly 10.8 MJ. Where the answer needs more digits than are shown, it carries the ≈ mark described in Numbers and percentages.

Convert

Type the amount, a conversion word, and the unit you want.

in, to, as and into all do the same thing. Names can be singular or plural, spelled out or short: km, kilometer, kilometers and kilometre are the same unit. The answer is written with the unit's short symbol, whatever you typed.

Because in is also the word for inches, spell the inch out when it is the target of a conversion: 72 inches in feet is 6 ft. Writing 12 in in cm also works (30.48 cm), but inch and inches read better.

Ask the other way round

Put the unit first and the quantity after to ask how many of a unit it holds:

Several units at once

Join units with and, or put them one after another, to split an amount into parts:

Going the other way, adjacent quantities are one amount: 5 feet 6 inches in cm is 167.64 cm, 5 lb 8 oz in kg is 2.494758035 kg, and 2 h 30 min in minutes is 150 min. Feet and inches typed together stay as words: 5 ft 6 in shows 5 feet 6 inches, and a part of a pound shows in ounces (13.5 lb is 13 lb 8 oz).

Pixels

Pixels, points, em and rem are lengths. A pixel is 1/96 inch, a point 1/72 inch, and an em or rem is 16 pixels, so 12 pt in px is 16px and 96 px in inches is 1 in. To count pixels at another density, add at N ppi: 1 in in px at 144 ppi is 144px.

Units Babbage knows

Examples, each checked: 1 hp in W is 745.6998715823 W, 1 metric hp in W is 735.49875 W, 100 kPa in psi is 14.503773773 psi, 1 atm in bar is 1.01325 bar, 1 cal in J is 4.184 J, 90 deg in rad is 1.5707963268 rad, and 1 hectare in acres is 2.4710538147 ac.

Some details worth knowing:

• Prefixed liters can be written with a capital or a small l: 5 ml and 5 mL are both 5 mL, and cl, dl and kl work the same way. 1.5 l alone is fine, and milliliters and millilitres work in full.
• The electrical prefixes print as the SI name: 5 mF is 5 mfarad, 5 uF and 5 µF are 5 µfarad, 5 mH is 5 mhenry, 5 mS is 5 msiemens and 5 mT is 5 mtesla.
• Gallons, quarts, pints, cups and fluid ounces are US measures. Put imperial or uk in front for the imperial ones: 1 imperial gallon in liters is 4.54609 L.
• ton is the short ton (2,000 lb) and tonne is 1,000 kg.
• hp is mechanical horsepower, exactly 550 ft·lbf per second. For the metric and electrical kinds write metric hp or cv (735.49875 W) and ehp (746 W).
• A month is 30.436875 days and a year is 365.2425 days, so 1 year in days is 365.2425 days. A workday is the work-hours setting, 8 hours unless you change it.
• Feet and inches can be written with marks: 5' 6" is 5 feet 6 inches, 6" is 6 inches, and 5' 6" + 2 inches is 5 feet 8 inches.
• rpm is revolutions per minute, so 60 rpm in rps is 1 rev/s.

Sums and products

A plain number takes the unit

A number beside a quantity in a sum becomes the same unit: 300 + 20 km and 20 km + 300 are both 320 km.

Two units of one kind

In a sum, the result is in the larger unit: 1 km + 500 m is 1.5 km, 500 m + 1 km is 1.5 km, and 5 mi + 3 km is 6.8641135767 mi. A quotient of two quantities of one kind has no unit left: 10 km / 2 km is 5.

Multiplying

A quantity times a plain number keeps its unit (2 km * 3 is 6 km). A length times a length is an area, in the left-hand unit squared: 10 m x 50 cm is 5 m², 6 ft x 4 ft is 24 ft², and 10 ft x 12 ft x 8 ft in m³ is 27.1841727283 m³. Other products keep every unit as you typed it: 3 kg * 2 m is 6 kg m, 3 kg m/s stays 3 kg m/s, and 1 W * 3 h is 3 W hour. Convert it to what you want: 2 kW * 3 h in kWh is 6 kWh.

Speeds and per-units

A speed is a length over a time, written with a slash, per, or the word over:

The unit comes back the way you wrote the hour. h stays km/h, while hours and hr after a slash read km/hour. Use a rate in a product and the time cancels. A bare unit after a slash belongs to the factor just before it, so 40 hours * $25 / hour is $1,000.00, the same as $25/hour * 40 hours:

at after a distance gives the time it takes. The same pattern prices things per unit; see Money.

Fuel economy

Fuel economy is distance per volume (mpg, US gallons) or volume per distance (L/100km). They convert into each other:

Multiply or divide fuel economy by what it measures and the units cancel:

Temperatures

Convert with C, F and K (or °C, °F, celsius, fahrenheit, kelvin):

A temperature is a point on a scale, so there are only a few things you can do with one besides converting it. You can add or subtract a plain number, a percentage or a temperature of the same scale, and multiply or divide by a plain number:

Mixing two scales (20 C + 5 F) is refused. Convert one first.

Data sizes

Babbage keeps the decimal and binary families apart, as the names do.

A byte is 8 bits. Case matters: MB is megabytes and Mb is megabits. The kilobyte is written kB, and KB is read as the same unit: 5 KB is 5 kB.

Transfer speeds and times

Mbps is megabits per second and MBps (or MB/s) is megabytes per second. Divide a size by a rate to get a time:

Mixing units and words

A word that is not a unit is skipped, so 10 km walked is 10 km. A word right after a plain number that is one letter away from a real unit gets a wavy underline, and the pointer over it shows "Did you mean km?" (5 kmm). If two units measure different things, the line says so: 1 kg in km is an error ("these units measure different things"). A unit Babbage does not know is skipped like any other word, and then the conversion is not done, so check that the answer ends in the unit you asked for.

Units also work inside variables and totals and with dates and times.