Speedcon - Speed Unit Converter
Speedcon converts a speed between seven units: kilometres per hour, metres per second, miles per hour, knots, feet per second, centimetres per second and Mach. Enter a number, pick the units, and the result appears on a speedometer-style gauge with up to six decimal places, or in scientific notation for very large or very small values.
Numbers are easier to grasp with context, so Speedcon also compares your speed with familiar fast things such as a high-speed train, a cruising airliner, the speed of sound and the International Space Station. Two more tabs turn the speed into physics figures for a one-tonne object and into the time needed to travel 100 kilometres.
It is useful for travel, sailing and aviation units, sports and running paces, physics homework, and simply satisfying curiosity. It runs in your browser with nothing to install.
The app runs entirely in your browser. What you enter is saved only on this device.
How to use Speedcon
- Enter a speed. Type a positive number in the value field. Negative values and text are rejected with a short message.
- Choose the units. Select the From and To units from the menus. The swap button in the middle reverses the direction.
- Read the result. The Conversion Result card shows the converted value and unit on a gauge. Tap the copy icon to copy it.
- Compare. Below the result, Speedcon names the closest reference speed and shows your value as a percentage of it.
- Explore the physics. Open the Physics tab for the kinetic energy of a 1,000 kg object, its theoretical braking distance on a dry road and the centripetal force in a 100 m radius turn.
- Check travel time. Open the Time tab to see how long 100 km takes at that speed, the estimated arrival time if you left now, and a rough fuel-use figure.
Features
- Seven units: km/h, m/s, mph, knot, ft/s, cm/s and Mach
- Swap button and copy-to-clipboard
- Speedometer-style result display
- Comparison with high-speed train, airliner, speed of sound and ISS
- Kinetic energy, braking distance and centripetal force
- Travel time and arrival time for 100 km
- Validation for invalid or negative input
Speed units and what they mean
The common units
Kilometres per hour is used on roads in most of the world, while miles per hour is used in the United States and the United Kingdom. Scientists and engineers prefer metres per second, the SI unit. One metre per second is exactly 3.6 km/h, and one mile per hour is about 1.609 km/h. Feet per second appears in ballistics and some engineering fields.
Knots and Mach
A knot is one nautical mile per hour, or exactly 1.852 km/h. It is the standard unit at sea and in aviation because nautical miles relate to latitude on charts. Mach expresses speed as a multiple of the speed of sound. The speed of sound depends on air temperature, so Mach 1 is not a fixed speed; Speedcon uses about 1,224 km/h, a common sea-level value, while at cruising altitude, where the air is colder, Mach 1 is closer to 1,060 km/h.
Why braking distance grows so fast
Kinetic energy rises with the square of speed. Doubling your speed means four times the energy for the brakes to absorb, and therefore roughly four times the braking distance. Speedcon's braking figure uses a friction coefficient of 0.7 for a dry road and ignores reaction time, so real stopping distances are longer: at 100 km/h a driver travels nearly 28 metres every second before even reaching the brake pedal.
Travel time and fuel
Travel time is simply distance divided by speed, but small changes in speed save less time than people expect on long journeys. Going from 100 to 110 km/h over 100 km saves only about five minutes. The fuel figure in Speedcon is a simplified model that is lowest around 80 km/h and rises at lower and higher speeds; treat it as an illustration of the trend, not a prediction for any particular vehicle.
Converting by hand
To go from km/h to m/s, divide by 3.6; from m/s to km/h, multiply by 3.6. From km/h to mph, multiply by about 0.621. From knots to km/h, multiply by 1.852. Keeping these four factors in mind covers most everyday conversions.
Frequently asked questions
What value does Speedcon use for Mach 1?
About 1,224 km/h, the speed of sound in air at sea level and around 15 °C. Real Mach numbers depend on temperature and altitude.
Are the physics results realistic?
They are textbook calculations for a 1,000 kg object: kinetic energy as one half m v squared, braking distance with a friction coefficient of 0.7 and no reaction time, and centripetal force in a 100 m turn. They are useful for learning, not for road safety decisions.
Why do some results appear in scientific notation?
Values smaller than 0.0001 or larger than 10,000 are shown in scientific notation, for example when converting a walking speed into Mach.
Is anything saved?
No. Conversions are calculated in your browser and are not stored. Reloading the page starts fresh.
Does it work offline?
An internet connection is needed to load the page. After that, conversions are calculated locally.
What is different from the phone app?
The converter is the same. The iPhone and Android apps show ads that a subscription removes; the web version has no ads or purchases.
Limitations of the web version
- Mach uses a fixed sea-level speed of sound
- Physics figures assume a 1,000 kg object and fixed conditions
- The fuel figure is a simplified illustration
- Results are not saved between visits
Phone app
Speedcon is also available as an app for phones and tablets: