A comprehensive reference for converting between metric, imperial, and specialized units across length, weight, temperature, volume, digital storage, CSS units, and cooking measurements.
Conversion of units is the conversion of the unit of measurement in which a quantity is expressed, typically through a multiplicative conversion factor that changes the unit without changing the quantity. This is also often loosely taken to include replacement of a quantity with a corresponding quantity that describes the same physical property.
Source: Wikipedia - Conversion of units
Content verified March 20, 2026
The metric system (International System of Units, or SI) was adopted by France in 1795 during the French Revolution. Its defining feature is base-10 relationships: 1 kilometer = 1,000 meters, 1 kilogram = 1,000 grams, 1 liter = 1,000 milliliters. This decimal structure makes conversion between units straightforward: just move the decimal point.
The imperial system, based on English units, uses non-decimal relationships: 1 mile = 5,280 feet, 1 pound = 16 ounces, 1 gallon = 4 quarts = 8 pints = 128 fluid ounces. These seemingly arbitrary numbers have historical origins (a foot was roughly the length of a human foot, a yard was the distance from nose to outstretched fingertip), but they make arithmetic conversion much harder than metric.
Today, only three countries have not officially adopted the metric system: the United States, Liberia, and Myanmar. Even in the US, metric is used in science, medicine, the military, and international trade. The dual system creates a constant need for conversion, which is why "convert X to Y" is one of the most common search query patterns on the internet.
| Quantity | Unit | Symbol |
|---|---|---|
| Length | meter | m |
| Mass | kilogram | kg |
| Time | second | s |
| Electric current | ampere | A |
| Temperature | kelvin | K |
| Amount of substance | mole | mol |
| Luminous intensity | candela | cd |
All other metric units are derived from these seven. Force (newton) = kg * m/s^2. Energy (joule) = kg * m^2/s^2. Pressure (pascal) = kg / (m * s^2). The entire system is self-consistent and interconnected.
Length is the most frequently converted measurement type. Here are the essential conversion factors:
| From | To | Multiply By |
|---|---|---|
| millimeters (mm) | centimeters (cm) | 0.1 |
| centimeters (cm) | meters (m) | 0.01 |
| meters (m) | kilometers (km) | 0.001 |
| micrometers (um) | millimeters (mm) | 0.001 |
| nanometers (nm) | micrometers (um) | 0.001 |
| From | To | Multiply By |
|---|---|---|
| inches (in) | feet (ft) | 0.08333 |
| feet (ft) | yards (yd) | 0.33333 |
| yards (yd) | miles (mi) | 0.000568 |
| feet (ft) | miles (mi) | 0.000189 |
| From | To | Multiply By | Quick Approximation |
|---|---|---|---|
| inches | centimeters | 2.54 | x 2.5 |
| feet | meters | 0.3048 | x 0.3 |
| miles | kilometers | 1.60934 | x 1.6 |
| centimeters | inches | 0.3937 | x 0.4 |
| meters | feet | 3.28084 | x 3.3 |
| kilometers | miles | 0.62137 | x 0.6 |
A useful mnemonic for miles to kilometers: Fibonacci numbers approximate the conversion. 1 mile is about 2 km, 2 miles is about 3 km, 3 miles is about 5 km, 5 miles is about 8 km, 8 miles is about 13 km. This works because the ratio of consecutive Fibonacci numbers approaches the golden ratio (1.618), which is close to the actual conversion factor of 1.609.
Convert between any length units with the Zovo Unit Converter. Supports metric, imperial, nautical, and astronomical units.
Strictly speaking, weight and mass are different physical quantities (mass is intrinsic; weight depends on gravitational field strength), but in everyday use they are treated interchangeably.
| From | To | Multiply By | Quick Approximation |
|---|---|---|---|
| pounds (lb) | kilograms (kg) | 0.453592 | Divide by 2.2 |
| kilograms (kg) | pounds (lb) | 2.20462 | Multiply by 2.2 |
| ounces (oz) | grams (g) | 28.3495 | Multiply by 28 |
| grams (g) | ounces (oz) | 0.03527 | Divide by 28 |
| stones (st) | kilograms (kg) | 6.35029 | Multiply by 6.35 |
| stones (st) | pounds (lb) | 14 | Exact |
| metric tons (t) | pounds (lb) | 2,204.62 | Multiply by 2,200 |
A quick mental trick for pounds to kilograms: halve the pounds and subtract 10%. So 150 lb = 75 - 7.5 = 67.5 kg (actual: 68.04 kg, error: 0.8%).
Troy ounces are used for precious metals and differ from standard (avoirdupois) ounces. One troy ounce = 31.1035 grams, compared to 28.3495 grams for a standard ounce. When gold prices are quoted as "$2,000 per ounce," they mean troy ounces. Gemstones use carats: 1 carat = 0.2 grams = 200 milligrams.
Temperature conversion involves formulas rather than simple multiplication because the scales have different zero points.
Celsius to Fahrenheit: F = (C x 9/5) + 32
Fahrenheit to Celsius: C = (F - 32) x 5/9
Celsius to Kelvin: K = C + 273.15
Kelvin to Celsius: C = K - 273.15
Fahrenheit to Kelvin: K = (F - 32) x 5/9 + 273.15| Description | Celsius | Fahrenheit | Kelvin |
|---|---|---|---|
| Absolute zero | -273.15 | -459.67 | 0 |
| Water freezes | 0 | 32 | 273.15 |
| Room temperature | 20-22 | 68-72 | 293-295 |
| Human body | 37 | 98.6 | 310.15 |
| Water boils (sea level) | 100 | 212 | 373.15 |
| Oven: Low | 150 | 300 | 423.15 |
| Oven: Moderate | 180 | 350 | 453.15 |
| Oven: Hot | 220 | 425 | 493.15 |
Quick mental conversion tricks: For Celsius to Fahrenheit, double the Celsius value and add 30 for a rough estimate. So 25C = (25 x 2) + 30 = 80F (actual: 77F). For Fahrenheit to Celsius, subtract 30 and halve: 80F = (80 - 30) / 2 = 25C (actual: 26.7C).
The two scales cross at -40 degrees: -40C = -40F. This is the only temperature where both scales read the same value.
Convert temperatures instantly with the Zovo Temperature Converter. Supports Celsius, Fahrenheit, Kelvin, and Rankine scales.
Volume conversions are complicated by the fact that the US customary system and the imperial system (used in the UK) define different sizes for gallons, pints, and fluid ounces.
| From | To | Multiply By |
|---|---|---|
| milliliters (mL) | liters (L) | 0.001 |
| liters (L) | cubic meters (m3) | 0.001 |
| microliters (uL) | milliliters (mL) | 0.001 |
| Unit | US Customary (mL) | Imperial (mL) | Difference |
|---|---|---|---|
| Fluid ounce | 29.574 | 28.413 | US is 4% larger |
| Cup | 236.588 | 284.131 | Imperial is 20% larger |
| Pint | 473.176 | 568.261 | Imperial is 20% larger |
| Quart | 946.353 | 1,136.52 | Imperial is 20% larger |
| Gallon | 3,785.41 | 4,546.09 | Imperial is 20% larger |
This difference matters when following recipes from different countries. A British pint of beer (568 mL) is 20% larger than an American pint (473 mL). If a British recipe calls for "1 pint of milk," using an American pint measure will give you too little.
| From | To | Multiply By |
|---|---|---|
| US gallons | liters | 3.78541 |
| liters | US gallons | 0.26417 |
| US cups | milliliters | 236.588 |
| milliliters | US cups | 0.00423 |
| US fluid ounces | milliliters | 29.574 |
| tablespoons | milliliters | 14.787 |
| teaspoons | milliliters | 4.929 |
Cooking conversions are among the most commonly searched conversion types. Here is a comprehensive reference:
| Measurement | Equivalent |
|---|---|
| 1 tablespoon (tbsp) | 3 teaspoons (tsp) |
| 1/4 cup | 4 tablespoons |
| 1/3 cup | 5 tablespoons + 1 teaspoon |
| 1/2 cup | 8 tablespoons |
| 1 cup | 16 tablespoons = 8 fluid ounces |
| 1 pint | 2 cups = 16 fluid ounces |
| 1 quart | 4 cups = 2 pints |
| 1 gallon | 16 cups = 4 quarts |
Professional bakers and European recipes use weight instead of volume because it is more precise. A cup of flour can vary from 120g to 160g depending on how it is scooped. Common ingredient weights:
| Ingredient | 1 US Cup (grams) |
|---|---|
| All-purpose flour | 125g |
| Granulated sugar | 200g |
| Brown sugar (packed) | 220g |
| Butter | 227g (2 sticks) |
| Water | 237g |
| Milk | 244g |
| Honey | 340g |
| Rice (uncooked) | 185g |
| Oats (rolled) | 90g |
Convert between cooking measurements with the Zovo Cooking Converter. Supports cups, tablespoons, teaspoons, milliliters, grams, and ounces with ingredient-specific densities.
Digital storage uses two different base systems, which causes confusion:
| Decimal (SI) | Value in Bytes | Binary (IEC) | Value in Bytes |
|---|---|---|---|
| 1 kilobyte (kB) | 1,000 | 1 kibibyte (KiB) | 1,024 |
| 1 megabyte (MB) | 1,000,000 | 1 mebibyte (MiB) | 1,048,576 |
| 1 gigabyte (GB) | 1,000,000,000 | 1 gibibyte (GiB) | 1,073,741,824 |
| 1 terabyte (TB) | 1,000,000,000,000 | 1 tebibyte (TiB) | 1,099,511,627,776 |
Hard drive manufacturers use decimal units (1 TB = 10^12 bytes), while operating systems report in binary units (1 TiB = 2^40 bytes). This is why a "1 TB" drive shows as approximately 931 GiB in your file manager. Neither side is wrong; they are using different unit definitions.
Network speeds are measured in bits per second (bps), while file sizes are in bytes. Since 1 byte = 8 bits, you need to divide the speed by 8 to estimate download times:
Convert between number systems with the Zovo Binary Converter. Supports binary, decimal, hexadecimal, and octal conversions.
Web developers frequently need to convert between CSS units. The most common conversion is pixels to rem units.
The rem unit is relative to the root element's font size, which defaults to 16px in all major browsers. To convert: rem = px / 16.
| Pixels | rem (at 16px base) | Common Use |
|---|---|---|
| 10px | 0.625rem | Small captions |
| 12px | 0.75rem | Small text, labels |
| 14px | 0.875rem | Secondary text |
| 16px | 1rem | Body text (default) |
| 18px | 1.125rem | Large body text |
| 20px | 1.25rem | H4 headings |
| 24px | 1.5rem | H3 headings |
| 28px | 1.75rem | H2 headings |
| 32px | 2rem | H1 headings |
| 48px | 3rem | Hero text |
| 64px | 4rem | Display headings |
Pixels are absolute units that do not scale with user preferences. If a user sets their browser's default font size to 20px (for accessibility), px-based layouts ignore this setting. Rem-based layouts scale proportionally. The WCAG 2.1 accessibility guidelines recommend using relative units for text sizing.
| Unit | Relative To | Common Use |
|---|---|---|
| em | Parent element font size | Component-level sizing |
| rem | Root element font size | Global sizing, spacing |
| vh | 1% of viewport height | Full-screen sections |
| vw | 1% of viewport width | Responsive text sizing |
| % | Parent element dimension | Fluid widths |
| ch | Width of "0" character | Max text width |
Convert CSS units with the Zovo px-to-rem Converter. Enter any pixel value and get the rem equivalent at your chosen base font size.
| From | To | Multiply By |
|---|---|---|
| mph | km/h | 1.60934 |
| km/h | mph | 0.62137 |
| m/s | km/h | 3.6 |
| km/h | m/s | 0.27778 |
| knots | km/h | 1.852 |
| knots | mph | 1.15078 |
| Mach 1 (sea level) | km/h | 1,234.8 |
| speed of light (c) | km/s | 299,792.458 |
For quick mph to km/h conversion, multiply by 1.6 or add 60% of the original value. 60 mph = 60 + 36 = 96 km/h (actual: 96.56 km/h).
| From | To | Multiply By |
|---|---|---|
| square feet (ft2) | square meters (m2) | 0.0929 |
| square meters (m2) | square feet (ft2) | 10.7639 |
| acres | hectares | 0.4047 |
| hectares | acres | 2.4711 |
| square miles | square kilometers | 2.5900 |
| square kilometers | square miles | 0.3861 |
| acres | square feet | 43,560 |
Useful reference points: A tennis court is approximately 260 m2 (2,800 ft2). A football field (excluding end zones) is about 4,459 m2 (48,000 ft2) or roughly 1.1 acres. A hectare is about 2.47 acres, and a square kilometer is 100 hectares.
Currency conversion differs from physical unit conversion because exchange rates change continuously. Unlike 1 inch always equaling 2.54 centimeters, 1 USD might equal 0.92 EUR today and 0.94 EUR tomorrow.
Key points about currency conversion:
Check current exchange rates with the Zovo Currency Converter. Updated rates for 150+ currencies with historical comparison.
Access all unit conversion tools from one place:
For developers implementing unit conversion in code:
For visual learners, search YouTube for "metric system explained" or "unit conversion tutorial" for channels like Khan Academy, Organic Chemistry Tutor, and Professor Dave Explains, which offer clear walkthrough videos for every conversion category covered in this guide.
| Feature | Chrome | Firefox | Safari | Edge |
|---|---|---|---|---|
| Intl.NumberFormat (locale formatting) | 24+ | 29+ | 10+ | 12+ |
| Input type="number" (numeric fields) | Full | Full | Full | Full |
| Clipboard API (copy results) | Full | Full | Partial | Full |
| Local Storage (save preferences) | Full | Full | Full | Full |
| Service Workers (offline use) | Full | Full | Full | Full |
Multiply the Celsius temperature by 9/5 (or 1.8) and add 32. The formula is F = (C x 1.8) + 32. For example, 25 degrees Celsius = (25 x 1.8) + 32 = 77 degrees Fahrenheit. For a quick estimate, double the Celsius value and add 30.
One mile equals 1.60934 kilometers. Multiply miles by 1.6 for a quick approximation. For the reverse, multiply kilometers by 0.6 to get miles. A fun trick: consecutive Fibonacci numbers approximate the conversion (3 miles is about 5 km, 5 miles is about 8 km).
Divide pounds by 2.2046 or multiply by 0.4536. For quick mental math, halve the pounds and subtract 10% of that result. Example: 180 lb = 90 - 9 = 81 kg (actual: 81.65 kg). For kilograms to pounds, multiply by 2.2.
The metric system uses base-10 units (meters, grams, liters) with consistent prefixes (kilo = 1,000, centi = 1/100, milli = 1/1,000). The imperial system uses non-decimal relationships (12 inches = 1 foot, 3 feet = 1 yard, 5,280 feet = 1 mile). Over 180 countries use metric; only the US, Liberia, and Myanmar primarily use imperial.
Divide the pixel value by the root font size (usually 16px). So 24px = 24/16 = 1.5rem. Common conversions: 12px = 0.75rem, 14px = 0.875rem, 16px = 1rem, 20px = 1.25rem, 32px = 2rem. Using rem units instead of pixels allows your layout to respect user font size preferences.
One liter equals approximately 4.227 US cups. For practical cooking purposes, treat 1 liter as 4 cups (the error is about 5.5%). Note that Imperial (UK) cups are larger: 1 liter equals about 3.52 Imperial cups. Always check whether a recipe uses US or UK measurements.
Binary to decimal: multiply each bit by 2 raised to its position power (right to left, starting at 0), then sum the results. Binary 1101 = (1x8) + (1x4) + (0x2) + (1x1) = 13. Decimal to binary: repeatedly divide by 2 and record remainders, reading from bottom to top.
It depends on the standard. Decimal (SI): 1 GB = 1,000,000,000 bytes (10^9), used by storage manufacturers. Binary (IEC): 1 GiB = 1,073,741,824 bytes (2^30), used by operating systems. This 7.4% difference is why a "500 GB" hard drive appears as about 465 GiB on your computer.
Want a video tutorial? Search YouTube for step-by-step video guides on unit conversion complete reference.