Speed Calculator — Free Online Speed Unit Converter

How to Use the Speed Calculator

1. Enter the speed value: Type the speed you want to convert into the Speed Value field. You can enter any positive number, including decimals like 65.5 or 3.14. The field accepts values from vehicle speeds to scientific measurements. Common starting points include highway speed limits (65 mph), wind speeds (25 km/h), or physics problems (9.8 m/s).
2. Select the source unit: Use the From Unit dropdown to choose the unit of your input value. The calculator supports five speed units: miles per hour (mph), kilometers per hour (km/h), meters per second (m/s), feet per second (ft/s), and knots (kn). Choose the unit that matches your original measurement.
3. View all conversions at once: Unlike calculators that convert between just two units, this tool instantly shows your speed in all four remaining units simultaneously. This is particularly useful when you need the same speed expressed in multiple systems, such as reporting wind speed in both km/h and knots for aviation weather reports.
4. Adjust and compare: Change the input value or source unit at any time to see updated results instantly. This real-time updating makes it easy to compare speeds across different units, build conversion tables, or quickly check multiple values for a project or assignment.

All conversions use internationally standardized conversion factors and display results with up to four decimal places for precision.

Speed Conversion Formulas

Variables Explained

• Miles per hour (mph): The standard speed unit in the United States and United Kingdom for road travel. One mile per hour equals 1.60934 kilometers per hour. Speed limits, vehicle speedometers, and weather reports in the US use this unit.
• Kilometers per hour (km/h): The standard speed unit in most countries worldwide. One kilometer per hour equals 0.621371 miles per hour. This is the metric system's primary speed unit for everyday use, appearing on road signs across Europe, Asia, South America, and Africa.
• Meters per second (m/s): The SI (International System of Units) standard for speed used in scientific and engineering contexts. One meter per second equals 3.6 km/h or 2.23694 mph. Physics formulas and scientific measurements universally use this unit.
• Feet per second (ft/s): Commonly used in US engineering, ballistics, and some sports applications. One foot per second equals 0.3048 m/s or 0.681818 mph. Bullet velocities and projectile speeds are often expressed in fps.
• Knots (kn): The standard speed unit in maritime and aviation industries worldwide. One knot equals one nautical mile per hour, or 1.852 km/h. Air traffic control, ship navigation, and weather reporting for marine and aviation use knots exclusively.

Step-by-Step Example

Convert 100 kilometers per hour to all other speed units:

1. Start with 100 km/h
2. Convert to m/s: 100 / 3.6 = 27.778 m/s
3. Convert to mph: 27.778 / 0.44704 = 62.137 mph
4. Convert to ft/s: 27.778 / 0.3048 = 91.134 ft/s
5. Convert to knots: 27.778 / 0.514444 = 53.996 knots

A speed of 100 km/h, which is a common highway speed limit in many countries, equals approximately 62.14 mph (just above the 60 mph speed limit common on US highways), 27.78 m/s, 91.13 ft/s, and 54.0 knots. The calculator performs all these conversions simultaneously through the intermediate step of converting to meters per second.

Practical Examples

Example 1: Anna's Road Trip from the US to Canada

Anna is driving from Detroit to Toronto and needs to understand Canadian speed limit signs, which are posted in km/h. The highway speed limit in Ontario is 100 km/h. She wants to know what speed to maintain on her mph speedometer:

• Input: 100 km/h
• Result: 62.14 mph
• City speed limit (50 km/h): 31.07 mph
• School zone (30 km/h): 18.64 mph

Anna sets a mental bookmark that 100 km/h is roughly 62 mph and 50 km/h is about 31 mph. She also notes that 120 km/h (the maximum posted speed on some Canadian highways) equals 74.56 mph, which feels more comfortable given her experience on US interstates.

Example 2: Carlos's Sailing Speed Conversion

Carlos is reviewing weather data for a sailing race. The marine forecast reports wind speeds in knots, but he wants to compare them with the km/h readings from his personal weather station at the marina:

• Forecast wind speed: 18 knots
• Converted: 33.34 km/h
• Also: 20.71 mph and 9.26 m/s

Carlos confirms that the 18-knot forecast matches the 33 km/h reading from his weather station. He also notes that gusts of 25 knots (46.3 km/h) are expected in the afternoon, which will require reefing the mainsail. Understanding the conversion helps him correlate official marine forecasts with his local instruments.

Example 3: Priya's Physics Lab Report

Priya is completing a physics lab where she measured the speed of a projectile as 152 feet per second using a chronograph. She needs to report the result in meters per second for her lab report and also wants to know the equivalent in km/h for context:

• Measured speed: 152 ft/s
• In m/s: 46.33 m/s (SI unit for the lab report)
• In km/h: 166.78 km/h (for intuitive context)
• In mph: 103.64 mph (additional reference)

Priya reports the projectile speed as 46.33 m/s in her lab report, noting for context that this is equivalent to about 167 km/h or 104 mph. This helps her professor and classmates understand the practical magnitude of the measurement, which is comparable to a professional tennis serve.

Example 4: James's Running Pace Conversion

James ran a 5K race and his GPS watch shows an average pace of 4.17 meters per second. He wants to know his speed in more familiar units to compare with treadmill settings and road running pace:

• GPS reading: 4.17 m/s
• In km/h: 15.01 km/h
• In mph: 9.33 mph
• Pace: approximately 6:26 per mile

James discovers his average speed was about 9.3 mph, which he can now set on the treadmill for interval training. At 15 km/h, he ran the 5K in approximately 20 minutes. He uses the speed converter to set training targets at different speeds, like 12 km/h (7.46 mph) for easy runs and 17 km/h (10.56 mph) for sprint intervals.

Speed Conversion Reference Table

Common speed values converted across all supported units. Values rounded to three decimal places.

Tips and Complete Guide

Quick Mental Conversion Tricks

For quick mental conversions between the most common speed units, use these approximations. To convert mph to km/h, multiply by 1.6 (or multiply by 8 and divide by 5 for more accuracy). To convert km/h to mph, multiply by 0.6 (or multiply by 5 and divide by 8). For m/s to km/h, multiply by 3.6. For knots to mph, multiply by 1.15. These rough conversions are accurate within 1% to 2% and are invaluable when traveling internationally, listening to weather forecasts in unfamiliar units, or doing quick calculations without a calculator. For instance, seeing a 130 km/h speed limit sign while driving in Germany, you can quickly estimate: 130 times 0.6 equals approximately 78 mph.

Speed Units in Different Industries

Different industries have standardized on specific speed units for historical and practical reasons. Aviation uses knots for airspeed and ground speed because of the direct relationship between nautical miles and latitude. Weather services use m/s for wind speed in scientific reports but often convert to mph or km/h for public forecasts. The automotive industry uses mph in the US and km/h elsewhere. Athletics and sports science often use m/s for sprint speeds and km/h for endurance sports. Engineering fields in the US frequently use ft/s, particularly in fluid dynamics, ballistics, and mechanical engineering. Understanding which unit is standard in your field prevents miscommunication and errors in technical work.

The Beaufort Wind Scale and Speed Conversions

The Beaufort scale classifies wind speed from Force 0 (calm, under 1 mph) to Force 12 (hurricane, over 73 mph). Understanding speed conversions helps interpret this scale across unit systems. Light breeze (Force 2) is 4 to 7 mph, which equals 6.4 to 11.3 km/h or 3.5 to 6.1 knots. A moderate gale (Force 7) is 32 to 38 mph, or 51.5 to 61.2 km/h, or 28 to 33 knots. Storm force (Force 10) is 55 to 63 mph, or 88.5 to 101.4 km/h, or 48 to 55 knots. These conversions are critical for sailors, pilots, outdoor event planners, and emergency management professionals who receive weather data in various unit systems and need to make safety decisions based on standardized thresholds.

Common Mistakes to Avoid

• Confusing nautical miles with statute miles: A nautical mile (1,852 meters) is about 15% longer than a statute mile (1,609 meters). Converting knots directly to mph without accounting for this difference leads to significant errors, especially over long distances.
• Forgetting that Mach varies with conditions: Mach 1 is not a fixed speed. It changes with temperature and altitude. At sea level, Mach 1 is about 767 mph, but at 35,000 feet it drops to about 660 mph. Always specify conditions when working with Mach numbers.
• Mixing up m/s and km/h: These metric units differ by a factor of 3.6, not a simple factor of 10 or 100. A value of 10 m/s is 36 km/h, not 10 km/h. This is a common error in physics homework and engineering calculations.
• Ignoring significant figures: When converting precise measurements, maintain appropriate significant figures. Converting 65.0 mph to km/h gives 104.607 km/h, but if the original measurement was only accurate to three significant figures, report 105 km/h.
• Using speed for pace calculations: Speed (distance per time) and pace (time per distance) are inversely related. A speed of 10 mph does not mean a pace of 10 minutes per mile. The pace is 6 minutes per mile (60 minutes divided by 10 mph).

Frequently Asked Questions