Speed Converter

Yes, the RoughTools Speed Converter is completely free with no account, subscription, or payment required. You can convert between km/h, mph, m/s, knots, and feet per second as many times as needed at no cost. RoughTools is funded through non-intrusive advertising, keeping every converter permanently free. There are no usage limits, no premium speed units behind a paywall, and no registration required.

No account, email address, or registration is required. Enter a value, select your source unit, and the converter instantly shows the equivalent in all supported speed units simultaneously. There is no login wall, no upgrade required to access any unit, and no data stored about your conversions. The converter is entirely anonymous and can be used unlimited times without any sign-up process.

No. All conversions run entirely within your browser using JavaScript. The values you enter are never transmitted to RoughTools servers, never logged, and never shared with any third party. Once you close the browser tab, all data is gone. Your speed calculations remain completely private — whether you are converting vehicle speeds, wind speeds, aircraft speeds, or scientific velocity values.

Yes, the converter is fully responsive and works on all modern smartphones and tablets. All input fields and the results panel are optimised for touch screens. This is useful when you are travelling between countries with different speed limit conventions, checking wind speed forecasts, comparing vehicle performance specifications, or studying physics problems on your mobile device.

The Speed Converter works in all modern browsers: Google Chrome, Mozilla Firefox, Microsoft Edge, Safari, Opera, and Brave on both desktop and mobile. No plugins or extensions are required. The converter uses standard JavaScript arithmetic that runs natively in every current browser. Any current version of Chrome, Firefox, or Safari on desktop or mobile is fully supported.

All conversion factors are exact or derived from exact definitions. One knot is exactly 1.852 km/h (as defined by the international standard). One mile is exactly 1.609344 km, so 1 mph equals exactly 1.609344 km/h. One m/s equals exactly 3.6 km/h. Feet per second derives from the exact foot definition: 1 ft/s = 0.3048 m/s = 1.09728 km/h. All conversions are precise to floating-point arithmetic limits — well beyond any practical measurement requirement.

Once the page has fully loaded in your browser, all conversions run in JavaScript without requiring an active internet connection. You can enter speed values and see all unit conversions offline after the initial page load. The initial page load requires internet access, but after that the converter functions entirely client-side. This is useful when reviewing route data, studying for exams, or working in locations without reliable connectivity.

To convert a speed: (1) Enter the numeric value in the input field. (2) Select the source unit — for example, km/h. (3) The results panel instantly shows the equivalent in all other units simultaneously: mph, m/s, knots, and feet per second. Results update in real time as you type. This is especially useful when comparing international speed limits, vehicle specifications, or weather data that uses different unit conventions in different countries.

Search engines convert between one pair of speed units at a time. RoughTools Speed Converter shows all supported units simultaneously in one view — enter a value in any unit and all others update instantly. This is far more efficient when you need to cross-reference km/h, mph, and knots at the same time — such as when reading a weather report (knots), checking a speed limit sign (mph or km/h), and looking up aviation data (knots) all at once.

To report a bug or request an additional unit — such as Mach number (speed of sound), furlongs per fortnight (humorous but valid), or centimeters per second — use the feedback link in the site footer or visit the RoughTools contact page. When reporting a bug, include the value and unit you entered, the browser and OS, and the incorrect result versus what you expected. Feature requests are reviewed and prioritised regularly.

Multiply km/h by 0.621371 to get mph. For example, 100 km/h × 0.621371 = 62.14 mph. To convert mph to km/h, multiply by 1.60934. A quick rule for mental maths: to convert km/h to mph, multiply by 5 and divide by 8. For example, 80 km/h × 5 ÷ 8 = 50 mph. Common road speed conversions: 30 km/h ≈ 18.6 mph, 50 km/h ≈ 31.1 mph, 60 km/h ≈ 37.3 mph, 100 km/h ≈ 62.1 mph, 120 km/h ≈ 74.6 mph.

A knot is one nautical mile per hour. One nautical mile equals exactly 1,852 meters, which is derived from one minute of arc of latitude on the Earth's surface — making nautical miles and knots naturally suited to navigation using coordinates. At one knot, a vessel or aircraft travels 1.852 km/h or approximately 1.151 mph. Knots are used in aviation and maritime navigation because they relate directly to the Earth's geographic coordinate system, simplifying course calculations and position plotting on nautical and aeronautical charts.