Free Online Tool

Unit Converter

Instantly convert between hundreds of units — length, weight, temperature, volume, speed, and more. No signup, no ads in the way.

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Length Converter

Convert meters, feet, inches, miles, km and more

From

Enter a value to see the conversion.

Quick Reference

From 1 unit	Equals

Why Use ToolStack?

ToolStack covers 9 measurement categories with hundreds of unit pairs. All conversions use precise formulas — no rounding errors, no approximations.

Metric vs. Imperial

Most of the world uses the metric system, but the US, UK, and a few others still use imperial. Our tool bridges both instantly so you never have to guess.

Built for Everyone

Whether you're a student doing homework, a traveler checking distances, or an engineer verifying specs — ToolStack is built to be fast and reliable.

100% Free, Always

No paywalls, no rate limits, no accounts. ToolStack runs entirely in your browser — all calculations happen locally on your device.

The Complete Guide to Unit Conversion

Unit conversion is one of the most practically useful mathematical skills, yet it is frequently the source of costly errors in engineering, medicine, cooking, travel, and science. The most catastrophic example: NASA's Mars Climate Orbiter was lost in 1999 because one engineering team used metric units while another used imperial — a $327 million mistake. Accurate unit conversion matters at every scale.

Metric vs Imperial Systems

The metric system (SI) is used by 95% of the world's population and is built on a decimal base — every unit scales by powers of 10. The imperial system (used primarily in the US, with remnants in the UK) uses irregular conversion factors (12 inches in a foot, 3 feet in a yard, 5,280 feet in a mile). For most everyday purposes in the US, you need to convert between these two systems regularly — especially for cooking, fitness, temperature, and international travel.

Temperature Conversion Quick Reference

Celsius to Fahrenheit: multiply by 9/5 and add 32. Fahrenheit to Celsius: subtract 32 and multiply by 5/9. Key reference points: 0°C = 32°F (water freezes), 100°C = 212°F (water boils), 37°C = 98.6°F (body temperature), 20°C = 68°F (comfortable room temperature). A quick mental shortcut: double the Celsius temperature and add 30 gives an approximate Fahrenheit value.

Frequently Asked Questions

How accurate are the conversions? ▾

All conversions use industry-standard formulas with full floating-point precision. For temperature, the exact formulas (e.g. °F = °C × 9/5 + 32) are used rather than rounded approximations. Results are displayed to up to 8 significant figures.

What's the difference between mass and weight? ▾

Mass measures the amount of matter in an object (kilograms, pounds) and doesn't change with gravity. Weight is a force (Newtons) that depends on gravity. In everyday usage, "weight" usually refers to mass — our converter handles all common mass units.

How do I convert Celsius to Fahrenheit? ▾

Use the Temperature tab above. The formula is: °F = (°C × 9/5) + 32. For example, 100°C = 212°F (boiling point of water). Common benchmarks: 0°C = 32°F (freezing), 37°C = 98.6°F (body temperature).

Can I use this on my phone? ▾

Yes! ToolStack is fully responsive and works on any device — phone, tablet, or desktop. No app download needed, just open it in your browser and convert instantly.

Why are some units not available? ▾

We focus on the most commonly used units in each category. If you need a specific unit that isn't listed, we're always adding more. For very specialized scientific units, we recommend checking NIST or a dedicated scientific converter.

How to Use the Unit Converter

Convert between metric and imperial units for length, weight, temperature, volume, speed, and area.

Select a category

Choose from Length, Weight, Temperature, Volume, Speed, or Area at the top. The available units update automatically.

Enter your value

Type the number you want to convert in either input field. Both fields update simultaneously — conversion works in both directions.

Select your units

Use the dropdowns to choose the 'from' and 'to' units. Common conversions like miles↔km and kg↔lbs are pre-selected for speed.

Copy the result

Click the result to copy it. Or leave both fields open and switch between units — useful for comparing multiple conversions quickly.

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💡 Cooking shortcut: 1 cup = 240ml, 1 tablespoon = 15ml, 1 teaspoon = 5ml. Temperature: subtract 32, multiply by 5/9 to convert °F to °C.