Free Unit Converter Online: Convert Length, Weight, Temperature & More in 2026
Whether you are following a recipe from another country, planning a road trip abroad, checking a package weight for shipping, or tackling a physics homework problem, unit conversion is one of those everyday tasks that catches everyone off guard. Remembering that one mile is 1.609 kilometers or that one kilogram equals 2.205 pounds is useful — but memorizing dozens of conversion factors across six different measurement categories is simply impractical.
That is exactly why we built the DopaBrain Unit Converter — a free, instant, browser-based tool that handles 40+ units across 6 categories so you never have to search for a formula again. In this guide, we will walk you through every supported unit, show you how to use the converter, provide a quick-reference table for the most common conversions, and explain the difference between metric and imperial systems.
Convert Units Instantly
Free, fast, and accurate — select a category, enter a number, and see results in real time
Open Unit Converter →Supported Units
The converter covers six measurement categories, each packed with the units people use most often in daily life, travel, cooking, fitness, and professional work. Here is a complete breakdown:
| Category | Units Included | Common Use Cases |
|---|---|---|
| Length | Kilometer, Meter, Centimeter, Millimeter, Mile, Yard, Foot, Inch, Pyeong | Travel distance, height, screen sizes, room dimensions |
| Weight | Kilogram, Gram, Milligram, Pound, Ounce, Stone, Don, Nyang | Cooking, shipping, fitness, body weight tracking |
| Temperature | Celsius, Fahrenheit, Kelvin | Weather, cooking, science, travel abroad |
| Volume | Liter, Milliliter, Gallon, Quart, Pint, Cup, Fluid Ounce, Tablespoon | Cooking recipes, fuel, beverage servings |
| Area | Square Meter, Square Kilometer, Square Foot, Acre, Hectare, Pyeong | Real estate, land measurement, flooring |
| Speed | km/h, mph, m/s, Knots | Driving, running pace, aviation, sailing |
How to Use the Converter
The DopaBrain Unit Converter is designed to be as simple as possible. There are no menus to navigate, no settings to configure, and no accounts to create. Here is how it works:
- Select a category. Tap one of the six tabs at the top: Length, Weight, Temperature, Volume, Area, or Speed. Each tab displays the relevant units for that category.
- Enter a value. Type any number into one of the input fields. The converter calculates and displays the equivalent values in all other units within that category instantly as you type.
- Use quick presets. For frequently used conversions (like 33 pyeong to square meters or body temperature in Celsius to Fahrenheit), tap one of the preset chips below the category tabs to get an instant result without typing.
- Swap units. Use the swap button between two input fields to quickly reverse the direction of conversion.
- Review history. The converter automatically saves your recent conversions so you can refer back to them without re-entering values.
The entire tool runs in your browser. Your data stays on your device — nothing is sent to a server, and no personal information is collected. It even works offline once the page has loaded, which makes it useful when traveling in areas with limited connectivity.
Common Conversions Quick Reference
While the converter handles the math for you, knowing a few key conversion factors can be handy for quick mental estimates. Here are the most commonly needed conversions:
| From | To | Factor | Example |
|---|---|---|---|
| 1 kilometer | Miles | × 0.6214 | 5 km = 3.107 mi |
| 1 mile | Kilometers | × 1.6093 | 10 mi = 16.093 km |
| 1 kilogram | Pounds | × 2.2046 | 70 kg = 154.32 lb |
| 1 pound | Kilograms | × 0.4536 | 150 lb = 68.04 kg |
| 1 inch | Centimeters | × 2.54 | 6 in = 15.24 cm |
| 1 liter | US Gallons | × 0.2642 | 4 L = 1.057 gal |
| 1 US gallon | Liters | × 3.7854 | 2 gal = 7.571 L |
| Celsius | Fahrenheit | (×9/5)+32 | 25°C = 77°F |
| Fahrenheit | Celsius | (−32)×5/9 | 98.6°F = 37°C |
| 1 pyeong | Square meters | × 3.3058 | 33 pyeong = 109.09 m² |
Mental Math Shortcuts
km to miles: Multiply by 0.6 (close enough for quick estimates). 100 km/h is roughly 60 mph.
kg to pounds: Double the number and add 10%. 80 kg ≈ 160 + 16 = 176 lb (actual: 176.4 lb).
Celsius to Fahrenheit: Double the Celsius value and add 30. 20°C ≈ 40 + 30 = 70°F (actual: 68°F).
Metric vs Imperial: Understanding the Two Systems
One of the most common sources of confusion in unit conversion is the split between the metric system (also called SI, the International System of Units) and the imperial system (sometimes called the US customary system). Here is what you need to know:
The Metric System
Used by the vast majority of the world — roughly 95% of the global population — the metric system is built on base-10 relationships. One kilometer is exactly 1,000 meters. One kilogram is exactly 1,000 grams. One liter is exactly 1,000 milliliters. This decimal structure makes calculations straightforward and reduces errors, which is why it is the standard in science, medicine, and international trade.
The Imperial System
Primarily used in the United States, the imperial system has historical roots in British measurement standards. Its conversion factors are irregular: 1 mile = 5,280 feet, 1 pound = 16 ounces, 1 gallon = 4 quarts = 8 pints. While these relationships seem arbitrary compared to the metric system, they are deeply embedded in American culture, construction standards, and everyday language.
Why Both Still Exist
Despite decades of metrication efforts, the United States has never fully adopted the metric system for everyday use. American road signs, grocery labels, weather forecasts, and building codes remain imperial. Meanwhile, science, the military, and most international-facing industries use metric. This dual reality means Americans — and anyone interacting with American products, recipes, or measurements — need to convert between systems regularly. Our unit converter makes that process effortless.
Tips for Accuracy
Getting the right number from a unit converter is easy. Getting the right answer for your specific situation requires a bit more thought. Here are practical tips to ensure your conversions are accurate and useful:
- Know your precision needs. Cooking a recipe? Rounding to one decimal place is fine. Machining a metal part? You may need four or more decimal places. The converter provides high-precision results — choose the level of rounding appropriate to your task.
- Watch out for US vs UK gallons. A US gallon is 3.785 liters, while an imperial (UK) gallon is 4.546 liters — a 20% difference. Always confirm which gallon a recipe or fuel economy figure is using.
- Temperature is not linear. Unlike length or weight conversions (which are simple multiplication), temperature conversion between Celsius and Fahrenheit involves both multiplication and addition. A 10-degree increase in Celsius is an 18-degree increase in Fahrenheit, not a fixed ratio.
- Double-check unit abbreviations. "oz" can mean fluid ounce (volume) or ounce (weight). "m" means meter, not mile. "mm" means millimeter, not million. Small misreadings lead to big errors.
- Use the history feature. If you are doing multiple related conversions (like converting an entire recipe), the converter's history log helps you keep track of all your results without having to write them down separately.
When You Need Conversions
Unit conversion comes up in more situations than most people realize. Here are the most common scenarios where having a reliable converter saves time and prevents costly mistakes:
- Cooking and baking: International recipes often use metric measurements (grams, milliliters, Celsius) while American kitchens work in cups, tablespoons, and Fahrenheit. Converting incorrectly can ruin a dish — 350°F is not 350°C.
- Travel: Speed limits, distances, weather temperatures, and fuel volumes all differ between metric and imperial countries. Understanding that 120 km/h equals about 75 mph or that 30°C means it is quite warm (86°F) helps you navigate comfortably abroad.
- Fitness and health: Many fitness apps and communities use different systems. Your gym might list weights in pounds while your health app tracks in kilograms. Our BMI calculator works hand-in-hand with the unit converter for body measurement tracking.
- Online shopping: Buying products from international sellers often means dealing with unfamiliar size charts and weight specifications. Use our shopping calculator alongside the unit converter for smarter purchase decisions.
- Real estate: In Korea, property sizes are commonly listed in pyeong rather than square meters. Our converter includes pyeong support, making it easy to compare listings with international standards.
- Education: Science, math, and engineering courses require fluency in unit conversion. Having a reliable tool for homework and exam preparation builds confidence and reduces errors.
Whatever your reason for converting, the goal is the same: get the right number without wasting time or making mistakes. A dedicated converter tool eliminates the friction of searching for formulas, doing manual arithmetic, and second-guessing whether you applied the right factor.
Start Converting Now
40+ units across 6 categories — instant results, zero signup, works offline
Unit Converter → BMI CalculatorFrequently Asked Questions
What units can I convert?
The converter supports over 40 units across six categories: length (km, miles, meters, feet, inches, cm, yards, pyeong), weight (kg, lbs, oz, grams, stones, don, nyang), temperature (Celsius, Fahrenheit, Kelvin), volume (liters, gallons, ml, cups, fluid ounces, tablespoons), area (m², ft², acres, hectares, pyeong), and speed (km/h, mph, m/s, knots). All conversions are instant and bidirectional.
How accurate is the unit converter?
The converter uses internationally recognized conversion factors from the International Bureau of Weights and Measures (BIPM). Results are computed to multiple decimal places. For everyday purposes — cooking, travel, fitness, shopping, and school work — the accuracy is excellent. For scientific or engineering applications requiring extreme precision, always verify with calibrated instruments and consider significant figures.
What is the difference between metric and imperial?
The metric system uses base-10 relationships (1 km = 1000 m, 1 kg = 1000 g) and is used by most of the world. The imperial system uses irregular conversion factors (1 mile = 5,280 feet, 1 pound = 16 ounces) and is primarily used in the United States. The metric system is simpler for calculations, while imperial units persist in American daily life, construction, and cooking.
Can I convert temperature?
Yes. The converter supports Celsius, Fahrenheit, and Kelvin. Temperature conversion is unique because it uses both multiplication and addition: °F = (°C × 9/5) + 32, and °C = (°F − 32) × 5/9. The tool handles these formulas automatically — just enter a temperature in any scale and see the others update instantly.
Is it free to use?
Completely free with no restrictions. No signup, no daily limit, no premium features locked behind a paywall. The converter runs entirely in your browser, works offline after the initial load, saves your conversion history locally on your device, and supports 12 languages. You can even add it to your home screen for quick access like a native app.