Ready to calculate
Select what to solve, enter two values, and click Calculate// enter any two values to calculate the third
Calculate speed, distance, or time instantly. Enter any two values and get the third result with unit conversion and formula breakdown.
Ready to calculate
Select what to solve, enter two values, and click CalculateClick Speed, Distance, or Time tab at the top depending on the unknown value.
Fill in the two fields shown. For time, enter hours, minutes, and seconds separately.
Pick the output unit from the dropdown before clicking Calculate.
Get instant results with unit conversions and step-by-step formula breakdown.
The Speed Distance Time Calculator solves the classic physics triangle: Speed = Distance ÷ Time. Give it any two values and it instantly computes the third, converting between km/h, mph, m/s, meters, miles, and more.
It uses the fundamental physics relationship: Speed = Distance ÷ Time. Rearranged, Distance = Speed × Time and Time = Distance ÷ Speed. All inputs are first converted to SI base units (m/s and meters) before calculation, then converted to your chosen output unit.
The calculator supports km/h (kilometres per hour), mph (miles per hour), m/s (metres per second), and knots (nautical miles per hour). All conversions happen automatically based on the units you select.
Time is entered using three separate fields for hours, minutes, and seconds. You don't need to fill all three — enter just what you know. For example, 1.5 hours can be entered as 1h 30m 0s, or 90 minutes as 0h 90m 0s.
Yes! Click the ⏱ Time tab, then enter a speed (with unit) and a distance (with unit). The result will display in hours, minutes, and seconds, along with decimal hours for reference.
Distance supports kilometres (km), miles (mi), metres (m), feet (ft), and nautical miles (nm). Mix and match units freely — the calculator handles all conversions internally.
Yes. Calculations are performed using JavaScript's 64-bit floating point arithmetic. Results are rounded to 4 significant figures for readability, but the underlying math is precise. For academic use, always verify with your instructor's preferred rounding rules.
This calculator computes average speed — the total distance divided by total time elapsed. Instantaneous speed is the speed at a single moment, which requires calculus (derivatives). For everyday use like road trips and pace tracking, average speed is what matters.
A knot equals one nautical mile per hour (approximately 1.852 km/h or 1.151 mph). Knots are the standard unit for aviation and maritime navigation. Use it when working with aircraft speeds, ship speeds, or weather data from marine forecasts.
Whether you're planning a road trip, studying for a physics exam, or tracking athletic performance, the relationship between speed, distance, and time is one of the most fundamental calculations in everyday life. This free online Speed Distance Time Calculator removes the guesswork — just enter any two values, choose your units, and get the third result immediately.
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The core formula is deceptively simple: Speed = Distance ÷ Time. From this single equation, two more are derived:
Together these three formulas form the classic "SDT triangle" taught in every introductory physics curriculum. The triangle is a memory aid: cover up the variable you want to find, and the remaining two show the operation to perform.
One of the most common sources of confusion in speed-distance-time problems is unit mismatch. If speed is in km/h but distance is in metres, the answer will be wildly wrong without proper conversion. This calculator handles all unit conversions internally, so you can mix units freely.
Speed units: km/h (kilometres per hour), mph (miles per hour), m/s (metres per second), knots (nautical miles per hour).
Distance units: kilometres (km), miles (mi), metres (m), feet (ft), nautical miles (nm).
Time: Entered in hours, minutes, and seconds — the calculator converts to a single decimal value before computing.
All conversions are based on internationally recognised constants: 1 mile = 1.609344 km, 1 nautical mile = 1.852 km, 1 foot = 0.3048 m.
Road trips and driving: Enter the distance to your destination and your average speed to find out how long the drive will take. Alternatively, if you need to arrive in a specific number of hours, calculate the required average speed.
Running and cycling pace: Athletes frequently need to convert between pace (time per unit distance) and speed (distance per unit time). Enter your race distance and target finish time to find the required average speed in km/h or mph.
Aviation: Airspeed is typically measured in knots. Enter a flight distance in nautical miles and airspeed in knots to estimate flight time — or use mph and miles for domestic US travel.
Physics homework: Whether it's a car accelerating down a ramp or a train leaving a station, the SDT formula is a staple of GCSE, A-level, and introductory university physics problems. This calculator provides the formula breakdown step by step, making it easy to check your work.
Maritime navigation: Ships use knots and nautical miles exclusively. This calculator supports both units natively, making passage planning straightforward.
After calculating, the results panel shows a step-by-step breakdown of how the answer was reached. This includes the conversion of each input to SI units (metres per second and metres), the calculation itself, and the conversion back to your chosen output unit. This transparency is particularly useful for students who need to show their working.
For example, solving for time given Speed = 60 mph and Distance = 120 miles:
It's important to understand that this calculator computes average speed: the total distance divided by the total elapsed time. It does not model acceleration, deceleration, or variable speed. If a car travels 100 km in 1 hour, its average speed is 100 km/h — even if it was stationary at traffic lights for part of that time and speeding on the motorway for another part.
Instantaneous speed — the speed at any precise moment — requires calculus (specifically, the derivative of position with respect to time) and is beyond the scope of a static calculator. For real-time speed measurement, use a GPS device or speedometer.
For the most accurate results, always ensure your inputs are as precise as possible. Use decimal values when needed — for example, 1.5 hours rather than rounding to 1 or 2 hours. When dealing with journeys that involve stops (like a road trip with rest breaks), enter only the actual moving time, not the total elapsed wall-clock time, unless you want to include stops in your average.
If you're working with very large values (astronomical distances, for instance), be aware that the result conversions displayed are rounded to 4 decimal places for readability. Copy the main result value for maximum precision.
Need more physics or measurement tools? The Unit Converter handles a comprehensive range of physical quantities beyond speed and distance. The Scientific Calculator is useful for more complex physics equations. For time-based planning, the Date Difference Calculator computes elapsed time between two calendar dates.