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How to convert cm to inches

To convert cm to inches, divide by 2.54. That number is exact: since 1959 one inch has been defined as 25.4 mm, so 170 cm ÷ 2.54 = 66.93 inches. For a height in feet and inches, divide the inches by 12. The whole number is feet and the remainder is inches, so 66.93 inches is 5 ft 6.93 in, which most people round to 5′7″.

Pick "Feet + inches" as the target unit above and the converter splits it for you. It works the other way too: type 5 and 11 into the feet and inches boxes and you get 180.34 cm.

Height chart: cm to feet and inches

How to convert kg to lbs

Multiply kilograms by 2.20462. The pound is defined as exactly 0.45359237 kg, so dividing by that number gives the same answer. 70 kg is 154.3 lb. In the UK body weight is often given in stone, and one stone is 14 lb, so 70 kg is 11 st 0.3 lb.

Going the other way, 150 lb × 0.45359237 = 68.04 kg. A rough mental shortcut is "halve it and take off 10%": 150 lb → 75 → 67.5 kg. It lands within about 1%.

Fahrenheit to Celsius (and back)

Subtract 32, then multiply by 5/9. So 100 °F is (100 − 32) × 5/9 = 37.8 °C. For Celsius to Fahrenheit, multiply by 9/5 and add 32: 37 °C is 98.6 °F. The two scales meet at −40, which is the same temperature in both.

The popular "subtract 30 and halve" trick is fine for weather but drifts badly at oven heats. It turns 350 °F into 160 °C, when the real figure is about 177 °C.

How many ml in a cup?

It depends whose cup. A US customary cup is 236.6 ml. Australia, Canada, New Zealand and many newer recipes use a metric cup of 250 ml, and US nutrition labels round a cup to 240 ml. Older British recipes sometimes mean an imperial cup of 284 ml. If a recipe comes from a US site, use the US cup; if it gives grams elsewhere on the page, trust the grams.

Spoons differ too. A US tablespoon is 14.79 ml and a metric one is 15 ml, close enough to ignore. The Australian tablespoon is 20 ml, so a tablespoon of baking powder in an Australian recipe is a third more than in a US one. US and UK fluid ounces also differ: 29.57 ml against 28.41 ml, and a UK pint holds 20 of them while a US pint holds 16.

km to miles and miles to km

Multiply kilometers by 0.621371, or divide by 1.609344 (the exact number of kilometers in a mile). Race distances are the usual reason people look this up:

• 5K = 3.107 miles
• 10K = 6.214 miles
• Half marathon, 21.0975 km = 13.109 miles
• Marathon, 42.195 km = 26.219 miles

For speed the factor is the same: 60 mph is 96.56 km/h and 100 km/h is 62.14 mph.

Feet to meters

Multiply feet by 0.3048. 6 feet is 1.8288 m, a 10-foot ceiling is 3.048 m, and 1 meter is 3.2808 feet. Square feet need the factor squared: 0.09290304 m² per ft², so a 1,000 ft² apartment is 92.9 m².

Why a 1 TB drive shows 931 GB

Drive makers use decimal units, where 1 TB is 10¹² bytes. Windows divides by 1024 at each step, so the same bytes come out as 931.3 GiB, which it labels "GB". macOS has used decimal units since 2009 and shows the full 1 TB. Choose KiB, MiB or GiB in the converter when you need the binary figure.

L/100 km and mpg are upside down

Liters per 100 km measures fuel used, while miles per gallon measures distance covered, so one goes down when the other goes up. You cannot multiply by a factor; you divide a constant by the figure. US mpg = 235.215 ÷ L/100 km, and UK mpg = 282.481 ÷ L/100 km, because the UK gallon is bigger. A car rated at 6.5 L/100 km does 36.2 mpg in the US and 43.5 mpg in the UK.

Sharing a conversion

The address bar updates as you type, for example #length/cm/in/170. Copy that link (or press "Copy link") and whoever opens it sees the same units and value. The table under the result lists the value in every unit of the category and can be copied or saved as a CSV file for a spreadsheet.

Frequently asked questions