How to Convert cm to Inches and kg to lbs (Metric vs Imperial)

By Syed M. Tahir · Published 2026-10-26 · 7 min read

Most of the world measures in centimetres and kilograms, while the United States, and the UK for some everyday uses, still uses inches, feet, pounds and ounces. If you shop online, sell to buyers abroad, follow recipes from another country or fill in forms that ask for height and weight, you will need to switch between the two systems. The good news is that the main conversions are exact and easy to remember. This guide explains the factors, shows how to convert by hand and in a spreadsheet, and covers the rounding and labelling mistakes that cause the most confusion.

Why the conversions are exact

Inches and pounds are not separate from the metric system any more. In 1959 the national standards laboratories of the United States, the United Kingdom, Canada, Australia, New Zealand and South Africa agreed on an international yard of exactly 0.9144 metres and an international pound of exactly 0.45359237 kilograms. Everything else follows from those two numbers:

• 1 inch = 1/36 of a yard = 2.54 cm exactly (25.4 mm)
• 1 foot = 12 inches = 30.48 cm
• 1 pound = 0.45359237 kg, and 1 ounce = 1/16 pound = 28.349523125 g

So when you convert 13 inches to 33.02 cm, that is not an approximation. Any rounding happens only when you shorten the answer. NIST, the US measurement institute, publishes these definitions in its unit tables, linked at the end of this guide.

How to convert cm to inches (and back)

inches = cm ÷ 2.54    cm = inches × 2.54

Examples: 30 cm ÷ 2.54 = 11.81 in. A 20 inch bag is 20 × 2.54 = 50.8 cm wide. For millimetres, multiply or divide by 25.4 instead.

A quick mental shortcut

To estimate inches from centimetres, multiply by 0.4 (or double, double again and divide by 10). 30 cm × 0.4 = 12, close to the exact 11.81. The shortcut slightly overstates the answer, by about 1.6%, so it is fine for a rough idea but not for a listing or a form.

Feet and inches

Heights and room sizes are often given in feet and inches. To convert centimetres:

1. Divide by 2.54 to get total inches: 170 cm ÷ 2.54 = 66.93 in.
2. Divide by 12 and keep the whole number as feet: 66.93 ÷ 12 = 5.58, so 5 feet.
3. Subtract those feet in inches to get the rest: 66.93 − 60 = 6.93 in.

The answer is 5 ft 6.93 in, usually rounded to 5 ft 7 in. A common mistake is to write 5.58 feet as "5 ft 58 in" or "5 ft 5.8 in". The decimal part is a fraction of a foot, not a number of inches.

Fractions of an inch

Tape measures and rulers in inches are marked in halves, quarters, eighths and sixteenths, not decimals. To turn a decimal into the nearest sixteenth, multiply the decimal part by 16 and round: 30 cm is 11.811 in, and 0.811 × 16 = 12.98, which rounds to 13/16. So 30 cm is about 11 13/16 inches. Use the unrounded decimal for this step, because rounding first can move the answer to the wrong sixteenth.

How to convert kg to lbs (and back)

pounds = kg ÷ 0.45359237 (about kg × 2.2046)    kg = pounds × 0.45359237

Examples: 1 kg = 2.2046 lb. 5 lb = 2.268 kg. For grams and ounces, 100 g = 3.527 oz and 1 oz = 28.35 g.

Pounds and ounces

Weights in the US are often written as pounds plus ounces. Take the whole pounds, then multiply the decimal part by 16. For 1.2 kg: 1.2 ÷ 0.45359237 = 2.6455 lb. The whole part is 2 lb, and 0.6455 × 16 = 10.33 oz, so the answer is 2 lb 10.33 oz.

A quick mental shortcut

To estimate pounds from kilograms, double the number and add 10%: 30 kg doubled is 60, plus 6 is 66 lb. The exact answer is 66.14 lb, so the shortcut is very close. To go from pounds to kilograms, halve the number and take away 10% of the result.

Stones

In the UK and Ireland, body weight is often given in stones and pounds. One stone is 14 pounds, or 6.35029318 kg. To convert 70 kg: 70 ÷ 0.45359237 = 154.32 lb, and 154.32 ÷ 14 = 11 stone with 0.32 lb left over, so 11 st 0.3 lb.

Volume: US and UK units differ

Length and weight units are shared between the US and the UK, but volume units are not. A US gallon is 3.785411784 litres, while a UK (imperial) gallon is 4.54609 litres, about 20% larger. A US pint holds 16 US fluid ounces, while a UK pint holds 20 UK fluid ounces, and even the fluid ounces differ slightly: about 29.57 ml in the US and 28.41 ml in the UK. Recipe cups vary too. The US customary cup is 8 US fluid ounces (about 236.6 ml), and many recipes from other countries use a 250 ml metric cup. When a recipe or a product label does not say which system it uses, look at where it comes from before converting.

Temperature

°F = °C × 9/5 + 32    °C = (°F − 32) × 5/9

Temperature cannot be converted with a single multiplier because the two scales have different zero points. Water freezes at 0 °C and 32 °F, and boils at 100 °C and 212 °F at standard sea-level pressure. For a rough estimate of Fahrenheit, double the Celsius figure and add 30: 20 °C gives about 70 °F (exactly 68 °F). The shortcut drifts further from the true value at oven temperatures, so use the exact formula for cooking.

Rounding: how precise should you be?

An exact conversion can produce more decimal places than the original measurement deserves. If you measured a bag as 33 cm with a tape measure, converting it to "12.992126 inches" suggests a precision you never had. A good rule is to keep about the same precision as the original: 33 cm becomes 13 in, and 33.5 cm becomes 13.2 in or 13 1/4 in. For things that must fit, such as rings, clothing or parts, round in the safe direction and say so, for example "fits wrists up to 7 in (17.8 cm)".

Converting in a spreadsheet

Both Microsoft Excel and Google Sheets have a CONVERT function, so you can convert a whole column of sizes at once:

• =CONVERT(13, "in", "cm") returns 33.02
• =CONVERT(2, "kg", "lbm") returns about 4.41 (the pound is written "lbm", for pound mass)
• =CONVERT(180, "C", "F") returns 356

Combine it with ROUND to control the decimals, for example =ROUND(CONVERT(A2, "cm", "in"), 1).

Common mistakes to avoid

• Dividing when you should multiply. Inches are bigger than centimetres, so the number of inches is always smaller. If your answer goes the wrong way, you used the wrong operation.
• Mixing US and UK volume units, especially gallons, pints and fluid ounces.
• Writing decimal feet as inches, such as 5.5 ft as "5 ft 5 in" instead of 5 ft 6 in.
• Converting rounded numbers again. Convert from the original measurement each time, rather than converting a rounded result back and forth.
• Labelling only one system. If buyers or readers come from several countries, show both, such as "13 in (33 cm)".

Our free unit converter does all of these conversions instantly, including feet and inches, pounds and ounces and tape-measure fractions. For other everyday maths, the percentage calculator and our guide on percentage increase and decrease may help.

Sources

• NIST Handbook 44, Appendix C: General Tables of Units of Measurement
• NIST: Refinement of values for the yard and the pound (1959 notice)
• NIST: Unit conversion
• Microsoft Support – CONVERT function (Excel)
• Google Docs Editors Help – CONVERT

This guide is general information for sellers and is not financial, tax or legal advice. Marketplace rules and fees change, so always confirm in your own seller account. DailyToolLab is not affiliated with Etsy Inc., Shopify Inc. or eBay Inc.