Speed Distance Time Calculator - Free Online Speed & Distance

What is the Speed-Distance-Time Relationship?

Speed, distance and time are three fundamental quantities in physics that are related by a simple formula. If you know any two of these values, you can always calculate the third. This relationship is the foundation of kinematics and is used in everyday life for travel planning, sports analysis, physics problems and engineering.

The Three Formulas

Examples

• Find Speed: A car travels 150 km in 2.5 hours. Speed = 150 ÷ 2.5 = 60 km/h
• Find Distance: A cyclist rides at 25 km/h for 3 hours. Distance = 25 × 3 = 75 km
• Find Time: A plane flies 800 km at 400 km/h. Time = 800 ÷ 400 = 2 hours
• With unit conversion: A runner averages 8 m/s for 100 metres. Time = 100 ÷ 8 = 12.5 seconds

Speed Units Explained

• km/h (kilometres per hour): Standard metric speed unit, used for road traffic in most countries.
• mph (miles per hour): Used for road traffic in the US, UK and a few other countries.
• m/s (metres per second): The SI unit of speed, commonly used in physics and science.
• knots: Equal to one nautical mile per hour, used in aviation and maritime navigation.

Tips & Tricks

• Quick km/h to m/s: Divide km/h by 3.6 to get m/s. E.g., 90 km/h ÷ 3.6 = 25 m/s.
• Quick mph to km/h: Multiply mph by 1.609. E.g., 60 mph × 1.609 ≈ 96.6 km/h.
• Average speed: For a round trip at different speeds, use the harmonic mean: 2ab / (a+b).
• Check units: Always ensure your distance and time units match your speed unit before calculating.

How This Calculator Works

1. Choose what to solve for: Speed, Distance or Time.
2. Enter the two known values: The third field is hidden since it will be calculated.
3. Select units: Pick from km/h, mph, m/s, knots for speed; km, mi, m, ft for distance; hours, minutes, seconds for time.
4. Instant result: The answer updates in real time as you type or change units.
5. Formula shown: The exact formula and calculation steps are displayed alongside the result.