Free Online Unit Converter
Free online unit converter with 12+ categories — length, mass, temperature, speed, volume, area, pressure, and DMS angles. Type naturally like "5 feet 6 inches to cm" and get instant results. Built on standard international conversion factors. No sign-up needed.
One Converter for Every Unit You'll Meet in STEM
This is a free online unit converter that handles 12+ measurement categories — from simple length conversions to complex DMS angle calculations. Converting units is something every student does — in physics lab, chemistry homework, engineering projects, and even cooking. This converter handles 12 categories in one place: length, mass, temperature, speed, volume, area, pressure, energy, power, time, angle (with DMS), and digital storage. Every conversion uses the standard international conversion factors, so the results match the values found in any reference textbook.
The smart input at the top lets you type naturally — 100 km to miles, 10 stone to kg, 55 mph to km/h — without hunting through dropdown menus. Each category has its own dedicated converter card with two-way swap and a button to send results directly to the main Calc84 calculator for further calculations.
Converting in Four Steps — No Button Hunting
- Choose a category. Pick from 12 conversion types — length, mass, temperature, volume, speed, area, pressure, energy, power, time, angle (DMS), or digital storage. Each card works independently, so you can run several conversions at the same time.
- Enter your value. Type any number in the input field. You can use decimals or scientific notation. The conversion runs instantly — no "Convert" button needed.
- Swap or send. Use the swap button (⇄) to flip the from and to units. Click the arrow (➜) to send the converted value to the main calculator for follow-up math. Need to convert in the other direction? Just swap.
- Use natural language (optional). The AI smart converter at the top understands plain English. Type "5ft 6in to cm", "bar to psi", or "32 Celsius to Fahrenheit" and it figures out the categories automatically.
Example: Chemistry & Ideal Gas Law
The Problem: You need to convert 2.5 atmospheres (atm) of pressure to kilopascals (kPa) to solve a PV=nRT chemistry equation.
- Scroll down to the Pressure conversion card.
- Ensure the left dropdown is set to Atmospheres (atm) and the right dropdown is set to Kilopascals (kPa).
- Type 2.5 into the input box. The tool instantly outputs the result: 253.3125 kPa.
- Click the ➜ (Send to Calculator) button to push this exact value to your main Calc84 graphing workspace so you can finish the rest of the equation without retyping long decimals.
Why Are There Two Measurement Systems?
Most of the world uses the metric system (meters, kilograms, liters). The United States uses US customary units (feet, pounds, gallons). The UK uses a mix of metric and imperial (stone for body weight, miles for roads, but meters for most everything else). This converter handles all three — metric, US customary, and imperial — so you can switch between them without doing mental math.
Metric units are based on powers of 10, which makes conversion easy: 1 kilometer = 1,000 meters, 1 kilogram = 1,000 grams, 1 liter = 1,000 milliliters. Imperial and US units use different ratios that are harder to remember: 1 mile = 5,280 feet, 1 gallon = 128 fluid ounces, 1 pound = 16 ounces. This is exactly why a converter is useful — nobody should have to memorize 5,280.
Temperature is a special case because the scales have different zero points. Celsius and Kelvin share the same degree size (1°C = 1K) but offset by 273.15. Fahrenheit uses a different degree size (1°F = 5/9°C) and a different zero point (water freezes at 32°F). The converter handles all three correctly — including the offset — so 0°C correctly converts to 32°F, not some wrong number from a broken formula.
What Are the Most Common Conversions?
| From | To | Conversion factor | Example |
|---|---|---|---|
| Inches | Centimeters | 1 in = 2.54 cm | 12 in = 30.48 cm |
| Feet | Meters | 1 ft = 0.3048 m | 6 ft = 1.8288 m |
| Miles | Kilometers | 1 mi = 1.60934 km | 100 mi = 160.934 km |
| Pounds | Kilograms | 1 lb = 0.45359 kg | 150 lb = 68.039 kg |
| Gallons (US) | Liters | 1 gal = 3.78541 L | 10 gal = 37.854 L |
| Fahrenheit | Celsius | °C = (°F − 32) × 5/9 | 98.6°F = 37°C |
| MPH | km/h | 1 mph = 1.60934 km/h | 60 mph = 96.56 km/h |
All of these conversions use the standard international conversion factors. For example, the length converter turns 1 meter into 3.28084 feet — the internationally agreed value. The angle DMS converter handles degrees-minutes-seconds to decimal and back, which is especially useful for surveying, navigation, and astronomy homework.
The Full Feature Set, Category by Category
- 12+ categories — length, mass, temperature, speed, volume, area, pressure, energy, power, time, angle (DMS), digital storage
- AI smart input — type "5ft 6in to cm" or "bar to psi" in plain English, no dropdowns needed
- DMS angle converter — degrees-minutes-seconds to decimal degrees and back
- Two-way swap on every category — flip from and to units with one click
- Send-to-calculator — push any converted value to the main Calc84 tool
- High precision — all conversion factors follow standard international reference values
- Works offline after first load — converts even without internet
Who Reaches for This Converter
Convert units for physics labs, chemistry homework, and engineering problem sets. The DMS angle converter handles surveying and astronomy calculations.
Demonstrate unit conversions on a smartboard. Use the natural language input to show students how to convert without memorizing formulas.
Quick conversions for construction, cooking, travel, and engineering, using the same standard factors any reference table uses.
Unit Conversion Questions, Answered
Is this unit converter free?
Yes, completely free. All 12+ categories — including DMS angles and compound unit conversions — work without signup, download, or payment. There are no limits on how many conversions you can run. It works offline after the first page load, so you can use it in a classroom with spotty Wi‑Fi.
How accurate are the conversions?
Every conversion uses double-precision arithmetic with the standard international conversion factors. The length converter produces 1 meter = 3.28084 feet — the internationally agreed value to five decimal places. Temperature conversions correctly handle the Fahrenheit-Celsius-Kelvin offsets, which many free converters get wrong.
Can this converter handle compound units like feet and inches?
Yes. The AI smart converter understands compound inputs. Type "5 feet 6 inches to cm" or "6 ft 2 in to meters" and it handles the addition automatically. This is useful for height conversions, construction measurements, and any situation where you have mixed units.
Does it convert angles in degrees-minutes-seconds (DMS)?
Yes. The angle converter handles DMS to decimal degrees and decimal to DMS in both directions. This is built for surveying, navigation, and astronomy students who regularly work with coordinates in degrees-minutes-seconds format.
Can I convert temperature between Celsius, Fahrenheit, and Kelvin?
Yes. The temperature converter correctly handles all three scales including the offset differences. Celsius and Kelvin share the same degree size but offset by 273.15. Fahrenheit uses a different degree size with a different zero point. The converter gets all three right every time.
How does the natural language input work?
Type what you want to convert in plain English — 100 km to miles, 5ft 6in to cm, or bar to psi. The AI smart converter figures out the categories automatically. No dropdowns needed. It understands compound units like "feet and inches" and handles them correctly.
Does it convert digital storage units?
Yes. Convert between bits, bytes, kilobytes, megabytes, gigabytes, and terabytes. Both decimal (1 KB = 1000 bytes) and binary (1 KiB = 1024 bytes) are supported. Useful for computer science students and anyone comparing file sizes or storage capacities.
Also useful: the graphing calculator plots functions for any unit-based data. The statistics calculator handles unit conversions within datasets for regression analysis. The equation solver works with unit conversions for physics and chemistry word problems. For the standards behind conversion factors, see NIST's metric system guide and the BIPM's SI reference for official unit definitions.
Page last updated: August 4, 2026
