Free Online Unit Converters
Convert between metric and imperial units instantly — centimeters to inches, kilograms to pounds, millimeters to inches, inches to centimeters, and feet to inches. Every converter runs entirely in your browser, so results appear the moment you type and nothing is ever uploaded.
Pick a converter to get started
Five focused tools, each built on the exact mathematical formula for its unit pair. No clutter, no advertising, no cookies.
CM to Inches Converter
Convert centimeters to inches with the international standard factor of 2.54 cm per inch. Ideal for clothing sizes, screen dimensions, and specifications that mix metric and imperial units.
KG to LBS Converter
Convert kilograms to pounds with the avoirdupois pound definition. Useful for body weight, gym plates, luggage limits, shipping manifests, and recipe scaling.
MM to Inches Converter
Convert millimeters to inches for drill bits, fasteners, 3D printing tolerances, PCB traces, plumbing, and engineering drawings where the two measurement systems meet.
Inches to CM Converter
Convert inches to centimeters exactly, since 2.54 is fixed by international agreement. Handy for screen diagonals, furniture dimensions, shoe sizes, and hobby measurements.
Feet to Inches Converter
Convert feet to inches with the exact 12-inch definition. Used for height records, US construction measurements, tape-measure readings, and hobby woodworking.
How Unit Conversion Works
A short, plain-language explanation of conversion factors, why direction matters, and how to verify any result by hand.
Convert any of the five units right here
Pick a conversion, type a value, and the result appears instantly. Nothing is stored, nothing is sent anywhere — all calculation happens on your device.
Popular conversions at a glance
A quick-reference table for the values people look up most often. Every number is derived from the same formula used by the interactive converter above, so the two can never disagree.
| Input | Result | Converter |
|---|---|---|
| 1 cm | 0.393701 in | cm to inches |
| 10 cm | 3.937008 in | cm to inches |
| 20 cm | 7.874016 in | cm to inches |
| 30 cm | 11.811024 in | cm to inches |
| 1 kg | 2.204623 lb | kg to lbs |
| 10 kg | 22.046226 lb | kg to lbs |
| 50 kg | 110.231131 lb | kg to lbs |
| 70 kg | 154.323584 lb | kg to lbs |
| 1 mm | 0.039370 in | mm to inches |
| 25 mm | 0.984252 in | mm to inches |
| 100 mm | 3.937008 in | mm to inches |
| 1 in | 2.54 cm | inches to cm |
| 12 in | 30.48 cm | inches to cm |
| 36 in | 91.44 cm | inches to cm |
| 1 ft | 12 in | feet to inches |
| 5 ft | 60 in | feet to inches |
| 6 ft | 72 in | feet to inches |
How unit conversion works
Every converter on this site is built on the same simple idea: a conversion factor that relates one unit to another. Understanding that idea lets you check any result, with or without a calculator.
1. A unit is an agreed amount
A centimeter, an inch, a kilogram, and a pound are all units — fixed, internationally agreed amounts used to describe a physical quantity. Because two different units can describe the same physical length or mass, converting between them is a matter of arithmetic, not guessing.
For example, a length of 1 inch is exactly the same physical distance as a length of 2.54 centimeters. Neither is "more correct". They are simply different labels for the same real-world amount.
2. The conversion factor
A conversion factor is a fixed number that tells you how many of one unit fit into another. For length, the exact international factors used on this site are:
| Relationship | Exact factor | Notes |
|---|---|---|
| 1 inch | = 2.54 centimeters | Fixed by the 1959 international yard and pound agreement |
| 1 inch | = 25.4 millimeters | Derived from the centimeter definition |
| 1 foot | = 12 inches | Fixed by definition, not by measurement |
| 1 pound | = 0.45359237 kilograms | International avoirdupois pound, exact |
| 1 kilogram | ≈ 2.2046226218 pounds | Reciprocal of the pound definition — a repeating decimal |
3. Multiply or divide — direction matters
The rule is simple. If you are moving to a smaller unit, the number gets bigger, and you multiply. If you are moving to a larger unit, the number gets smaller, and you divide.
- Inches to centimeters: centimeters are smaller, so multiply by 2.54. 10 in × 2.54 = 25.4 cm.
- Centimeters to inches: inches are larger, so divide by 2.54. 10 cm ÷ 2.54 = 3.937008 in.
- Feet to inches: inches are smaller, so multiply by 12. 5 ft × 12 = 60 in.
- Kilograms to pounds: pounds are smaller, so multiply by 2.2046… 10 kg × 2.2046226218 = 22.046226 lb.
4. Multiply and divide are exact inverses
Because multiply and divide are opposite operations, converting a value and then converting it back should return the original number. This is the quickest sanity check available. For example:
Round-trip verification
Start: 72 inches Convert to cm: 72 × 2.54 = 182.88 cm Convert back: 182.88 ÷ 2.54 = 72 inches ✓
5. Why some conversions are exact and others are not
Two of the converters on this site — inches to centimeters and feet to inches — are always exact for any input you can type. That is because the multiplier (2.54 and 12) is a fixed definition, and multiplying by it does not introduce any new error.
The other three involve a division, and division of an integer by 2.54 or 25.4 or 0.45359237 often produces a decimal that goes on forever. In those cases the site keeps every digit the computer can hold, and only rounds when it is time to show you the answer. You can read more about this in the accuracy and rounding section.
6. SI and imperial units side by side
The metric system (SI) is built on powers of ten, which is why centimeters, millimeters, and kilometers convert to one another by moving a decimal point. The imperial system, used daily in the United States and informally elsewhere, has its own historical relationships — twelve inches to a foot, three feet to a yard, sixteen ounces to a pound. This site handles both families and the bridges between them.
Accuracy and rounding, explained
Every number that appears on this site is calculated at full computer precision. Rounding is only ever applied when the value is written to the screen, so the underlying answer never drifts.
Full precision, inside and out
Modern web browsers store decimal numbers using the IEEE-754 double
format, which holds about fifteen to seventeen significant decimal
digits. Every calculation on this site uses that format, including
factors such as 2.2046226218487757 that are never
truncated before the arithmetic runs.
Display precision, by default
The converter shows 6 decimal places by default,
with trailing zeros trimmed. So a value of exactly one inch is shown
as 1 rather than 1.000000, and a value of
0.5 inches is shown as 0.5 rather than
0.500000.
You can raise or lower the display precision on any converter using the precision selector, from 0 to 12 decimal places. Changing the display precision never changes the internal value — it only changes the text shown to you.
When you should round yourself
For most real-world uses, the raw six-decimal output is more precise than you need. The following guidelines apply to everyday work:
| Use case | Suggested rounding | Example |
|---|---|---|
| Body height or weight | 1 decimal place | 172.5 cm · 70.3 kg |
| Sewing, carpentry, hobby projects | Nearest 1/16 inch or 1 mm | 0.0625 in · 1 mm |
| Shipping and luggage | 1 decimal place | 23.0 kg · 50.7 lb |
| Engineering and 3D printing | Nearest 0.001 mm or 0.0001 in | 0.254 mm · 0.0100 in |
| Screen diagonals and product spec sheets | 1 decimal place in the smaller unit | 55.9 cm · 22.0 in |
How to verify any result yourself
Every converter on this site states the formula it uses directly below the result. To check a result by hand, apply that formula with a calculator. The only difference you will see is that a hand calculator may show fewer decimal places than the site.
Verify 20 kg in pounds
Formula: pounds = kilograms × 2.2046226218487757 Substitute: pounds = 20 × 2.2046226218487757 Multiply: pounds = 44.092452436975514 Displayed: 44.092452 lb (6 decimals, trailing zeros trimmed)
What this site does not do
The converters do not adjust for local conventions such as US survey feet, and they do not attempt to convert between units of different physical kinds (for example kilograms to liters, which would require a density). Every converter on the site converts between units of the same physical quantity, and every stated factor is the one defined by the relevant international agreement.
Frequently asked questions
Short, direct answers to the questions people ask most often about the converters on this site.
Are the M-Convert converters really free?
Yes — every converter on M-Convert is completely free and requires no account, no email address, and no payment.
There is no paywall, no trial limit, and no advertising on the site. The converters run entirely inside your browser, so there are also no servers to maintain on your behalf and no usage limits to hit. You can open any converter page, close it, and open it again as many times as you like.
Do the converters work offline?
Yes — once the page has loaded, every converter keeps working even without an internet connection.
All calculation code is bundled with the site and runs on your device. Nothing is sent to a server, which means the converters continue to function when you lose signal, are on a plane, or deliberately go offline. The only reason you would need a connection again is to load a fresh copy of the page from Cloudflare's network.
How accurate are the results?
Every result is calculated at full computer precision — about 15 to 17 significant decimal digits — and only rounded when displayed.
Internal calculations are never truncated. The factors used (2.54 for the inch, 12 for the foot, 0.45359237 for the pound) are the exact international definitions. Where a conversion involves division, the site retains every digit the computer can hold and rounds only at the final display step. You can change the display precision from 0 to 12 decimal places on any converter page.
Why does my calculator show a slightly different number?
Your calculator is likely rounding earlier than M-Convert does, or displaying fewer decimal places.
Many pocket calculators and spreadsheet cells round intermediate steps. M-Convert does not — every digit is retained until the result is written to the screen. If you apply the same formula with full precision on a scientific calculator, you will get the same number this site shows.
Can I convert a negative value?
Yes — negative values are converted mathematically, and the site shows a short note explaining that physical lengths and masses are normally positive.
For example, entering −5 centimeters produces −1.968504 inches. This is the mathematically correct result, but a physical length or mass is rarely negative, so the note is there to prevent confusion when a negative input is entered by accident.
Do you store anything I type?
No — nothing you type is ever sent anywhere, and nothing is saved to your device by the converters.
The site is built as a static application. There is no backend, no database, and no analytics code. Every calculation happens inside the browser tab you are looking at, and that data disappears the moment you close the tab.
Can I use M-Convert on my phone?
Yes — the site is designed mobile-first and works on Android phones, iPhones, tablets, laptops, and desktop computers.
Touch targets are sized for fingers, the layout reflows cleanly from 320 pixels wide upward, and the converter keeps working when you rotate your device. Nothing is hidden behind a hover-only interaction, and every button is reachable by keyboard on larger devices.
Where does the conversion data come from?
Every factor used on this site is taken from the international definitions established by the 1959 yard and pound agreement.
That agreement fixed the international inch at exactly 2.54 centimeters and the international avoirdupois pound at exactly 0.45359237 kilograms. The foot is defined as exactly 12 inches by long-standing convention. These values are quoted directly in every formula shown on the site, so you can verify any result yourself.
Every converter on M-Convert
Direct links to each converter, with a one-line reminder of what each one does.
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CM to Inches Converter
Divide any centimeter value by 2.54 to get the equivalent number of inches.
-
KG to LBS Converter
Multiply any kilogram value by 2.2046226218 to get the equivalent number of pounds.
-
MM to Inches Converter
Divide any millimeter value by 25.4 to get the equivalent number of inches.
-
Inches to CM Converter
Multiply any inch value by 2.54 to get the equivalent number of centimeters exactly.
-
Feet to Inches Converter
Multiply any feet value by 12 to get the equivalent number of inches exactly.