Updated Unit Conversion Tool

Speed Converter

Convert speeds between m/s, km/h, mph, ft/s, knots and Mach. Use the main converter for everyday units, the Mach tab for altitude-aware conversions and the custom unit panel when you work with special speed units or scalings.

m/s ↔ km/h ↔ mph Feet per Second Knots & Mach Altitude Effects

Convert Between Common Speed Units And Mach Number

This Speed Converter lets you move quickly between meters per second, kilometers per hour, miles per hour, feet per second and knots. The advanced Mach tab takes into account the change in speed of sound with altitude, so you can convert between speed and Mach number under standard atmosphere conditions. A custom unit panel lets you define your own speed scale using a simple multiplier relative to m/s.

The main converter uses meters per second as an internal base unit and precise conversion factors for km/h, mph, ft/s and knots. The Mach tab uses a standard-atmosphere model to estimate the local speed of sound at a given altitude before converting between speed and Mach number.

Choose the input and output units and click convert. The calculator internally converts the input to m/s and then to the requested unit using fixed exact conversion factors.

Custom Speed Unit Converter

Use this panel to define a custom speed unit as a fixed multiple of meters per second. For example, if 1 custom unit equals 10 m/s, enter 10 as the multiplier.

The calculator uses a standard-atmosphere model for the troposphere to estimate the local speed of sound based on temperature at altitude. At sea level the speed of sound is 340 m/s and decreases with height until the tropopause.

This reference table shows selected speeds in m/s, km/h, mph and knots. Use it to develop a feel for typical magnitudes and to cross-check manually computed conversions.

The formulas below show the conversion factors used by the Speed Converter, including the relationship between everyday speed units and Mach number in a standard atmosphere.

Core Speed Conversion Factors

Unit Symbol Conversion to m/s
Meters per second m/s 1 m/s = 1 m/s
Kilometers per hour km/h 1 km/h = 1000/3600 m/s ≈ 0.27778 m/s
Miles per hour mph 1 mph ≈ 0.44704 m/s
Feet per second ft/s 1 ft/s ≈ 0.3048 m/s
Knots kt 1 kt ≈ 0.514444 m/s

Once a speed is converted to m/s using the table above, it can be converted to any other unit by dividing by the corresponding factor. For example, v(km/h) = v(m/s) ÷ 0.27778 and v(mph) = v(m/s) ÷ 0.44704.

Mach Number And Speed Of Sound

Mach number is the ratio between the true airspeed and the local speed of sound. In symbols,

M = v / a,

where v is the speed of the object and a is the speed of sound in the surrounding medium. In a standard atmosphere the speed of sound depends primarily on temperature. Within the troposphere an approximate model is

T(h) ≈ 288.15 − 0.0065 h,

where T is in kelvins and h is altitude in meters. The speed of sound is then

a = √(γ R T),

with γ ≈ 1.4 for air and R ≈ 287 J/(kg·K). The Mach tab uses this model, clamped to a reasonable range of altitudes, to estimate a and then convert between v and M in the chosen speed unit.

What Speed Converter Calculates

Use Speed Converter to convert speeds between m/s, km/h, mph, ft/s, knots and Mach.

Technology Calculators groups other calculations in the same subject.

Speed Converter Inputs

Speed Converter uses Speed value, From unit, To unit, Custom unit label, 1 custom unit = m/s.

Speed Converter Formula or Method

  • Internally, the tool uses a standard-atmosphere temperature profile in the troposphere and computes the speed of sound from that temperature. It then applies the formula M = v/a or v = M × a in the selected speed unit.
  • At high speeds, especially in aviation, the Mach number becomes more relevant than a raw speed. Mach is a dimensionless ratio defined as M = v / a, where v is the true airspeed and a is the local speed of sound. Because a depends on temperature, and temperature generally changes with altitude, the same Mach number corresponds to different true airspeeds at different heights.
  • The factors used by the Speed Converter are based on exact definitions such as 1 mile = 1609.344 meters and 1 nautical mile = 1852 meters. The displayed results are rounded to a fixed number of decimal places for readability, so minor differences can appear when comparing with other calculators that round differently, but the underlying relationships are consistent and precise.

Reading Speed Converter Results

The results include Converted speed, Base speed in m/s, All units overview, Conversion formula, Result, Equivalent in m/s.

Alongside Speed Converter, use Unit Converter to convert between hundreds of units across length, mass, temperature, time, volume, speed, data, pressure, energy, power and more.

For a different result from Speed Converter, Internet Speed Difference Calculator can compare two internet speeds side by side or analyze an ISP upgrade with download, upload and ping changes.

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After checking Speed Converter, use Unit Converter Calculator to convert between units of length, weight, temperature, speed, area, volume, time, energy, pressure and digital storage. When you need to estimate how long a file will take to download based on its size and your internet speed, use Download Time Calculator. Unit Conversion Calculator covers a separate task: convert length, area, volume, weight, temperature, speed and data units between metric, imperial, US and UK systems in one place.

After checking Speed Converter, use Timestamp Converter for Unix Time & Time Zones to convert Unix timestamps in seconds or milliseconds, switch between local and UTC displays, convert dates back to timestamps, and check the current epoch time. When you need to estimate how much bandwidth you need, how long downloads and uploads take, and convert data rates and file sizes using both metric (MB, GB) and binary (MiB, use Bandwidth Calculator. Conversion Calculator covers a separate task: convert values across length, weight, temperature, speed and other measurement categories using built-in unit conversion factors.

After checking Speed Converter, use File Size Calculator to convert between bytes, KB, MB, GB, TB and PB in one place.

Frequently Asked Questions About Speed Converter

It is used to convert speeds between m/s, km/h, mph, ft/s, knots and Mach.

It uses Speed value, From unit, To unit, Custom unit label, 1 custom unit = m/s.

Speed Converter uses Internally, the tool uses a standard-atmosphere temperature profile in the troposphere and computes the speed of sound from that temperature.

It returns Converted speed, Base speed in m/s, All units overview, Conversion formula, Result, Equivalent in m/s.

Check Speed value, From unit, To unit first. Differences can also come from rounding, unit choices, or a different formula or rule set.