Why use this calculator
Speed, distance and time are locked together by one relationship, and nearly every practical question about a journey is one of the three unknowns. A driver wants an arrival time, a runner wants the pace that produces a target finish, a skipper wants the speed that makes the tide gate, and a physics student wants the average speed implied by a distance-time graph.
Doing it in your head is easy to get wrong for one reason: the units almost never match. Distances arrive in kilometres, speed limits in miles per hour and durations in minutes, and mixing them silently produces an answer that is out by a factor of sixty.
This calculator converts every input to metres and seconds before dividing, so the unit mix on screen cannot corrupt the arithmetic, then hands the result back in every unit you might need to quote.
How to use it
- Start by choosing what you want solved, because that decides which two of the three values the calculator reads and which one it ignores.
- Enter the distance from a route planner, a race entry or your odometer, and set the distance unit to match the number you typed rather than converting first.
- Enter the time as a single number in one unit, so ninety minutes is 90 with minutes selected, never 1.5.
- Enter the speed you realistically expect to average, which on a road trip means something below the posted limit once fuel and coffee stops are counted.
- Set the speed unit to whatever your speedometer, GPS or flight plan shows, then read the converted equivalents underneath.
What each result means
- Speed
- The average speed over the whole journey, expressed in the speed unit you selected above.
- Distance
- The ground covered, converted back into the distance unit you chose for your input.
- Time
- The elapsed time for the journey in your chosen time unit, including any time spent stationary.
- Time as hours, minutes and seconds
- The same duration written the way a clock or a race result would show it.
- Speed in km/h
- The metric road speed, which is what signs and speedometers show across most of the world.
- Speed in mph
- The same speed in miles per hour for the United States and the United Kingdom.
- Speed in m/s
- The SI form of speed, which is the unit every physics formula expects you to supply.
- Pace per kilometre
- Minutes and seconds to cover one kilometre, the figure runners and cyclists actually train to.
- Pace per mile
- Minutes and seconds per mile, used by race organisers and runners in the US and UK.
The formula
Speed = distance / time
Distance = speed × time
Time = distance / speed
Internally distance is in metres (m), time in seconds (s) and speed in metres per second (m/s). One kilometre is 1,000 m, one statute mile is exactly 1,609.344 m and one nautical mile is exactly 1,852 m. One hour is 3,600 s, so a speed in m/s becomes km/h when multiplied by 3.6, and one mile per hour is exactly 0.44704 m/s.
Pace is the reciprocal of speed: seconds per kilometre = 1,000 / speed in m/s
How this number is used in practice
Trip planning is the everyday use, and the trap is confusing the posted limit with the speed you will average. Over a 600 km drive, a 100 km/h limit rarely produces better than an 85 km/h door-to-door average once you include fuel, food and roadworks, which is the difference between a six-hour day and a seven-hour one.
Freight operators and delivery planners build schedules from measured averages for exactly this reason, and the table of journey times at different speeds shows why pushing the average from 100 to 110 km/h saves far less than most drivers expect.
Athletes work the same relationship from the other end. A runner targeting a 3 hour 30 minute marathon divides 42.195 km into 210 minutes and gets a required pace of 4:59 per kilometre, then trains at that pace until it becomes automatic. Sailors and pilots use it with an extra twist, because their speed through the water or air is not their speed over the ground: a 6 knot boat punching into a 2 knot tide makes good only 4 knots, so the time answer has to be worked from ground speed rather than from the log.
Worked examples
100 km covered in 90 minutes
An average of 66.67 km/h, which is 41.42 mph or 18.519 m/s.
Driving 3.5 hours at an average of 95 km/h
Distance covered is 332.50 km.
A 42.195 km marathon held at 12 km/h
Finish time of 3.52 hours, which is 3h 30m 59s on the clock.
When people use it
- Estimating arrival time for a long drive from a realistic average speed
- Converting a target race time into the pace per kilometre you must hold
- Checking a flight or sailing plan where ground speed differs from indicated speed
- Working out the average speed a distance-time graph implies for a physics assignment
- Comparing whether a faster route or a shorter one actually gets you there sooner
Tips
- Average speed is total distance divided by total time, including every stop. It is never the average of the speeds you drove.
- Convert mph to km/h by multiplying by 1.609344; going the other way multiply km/h by 0.621371.
- For mental arithmetic, m/s to km/h is a multiply by 3.6, so 10 m/s is a brisk 36 km/h.
- Halving a journey time means doubling the speed, which is why shaving minutes off a long drive costs a dangerous amount of speed.
- Enter minutes as minutes, not decimal hours. Typing 1.5 with minutes selected asks for a journey of ninety seconds.
- A knot is one nautical mile per hour, which is 1.852 km/h exactly. Marine and aviation speeds are almost always in knots.
What it assumes, and where it stops being accurate
- The speed is treated as constant, so the answer is an average and not the speed at any single moment.
- Acceleration, braking, hills, traffic lights and headwinds are ignored. Real journeys run slower than the ideal figure.
- Distance is taken as the actual path travelled, not the straight-line distance between the two points.
- For marine and aviation use this solves ground speed only; current, tide and wind must be applied before you enter a speed.
- Relativistic effects are ignored, which is harmless below a few million metres per second but wrong for particle physics.
Terms used on this page
- Average speed
- Total distance divided by total elapsed time, including stops.
- Pace
- The inverse of speed: the time taken to cover one kilometre or one mile.
- Knot
- One nautical mile per hour, equal to 1.852 km/h exactly.
- Ground speed
- Speed relative to the ground, after current, tide or wind has been applied.
Questions people ask
- How do I convert mph to km/h?
- Multiply miles per hour by 1.609344, so 60 mph is 96.56 km/h. Going the other way, multiply km/h by 0.621371. For a quick road-sign estimate, adding about sixty per cent to a mph figure gets you close enough, and the calculator shows both conversions for every result it produces.
- Why is my real journey slower than the calculated time?
- Because this works from an average speed and a real trip is never run at a constant speed. Traffic lights, roundabouts, merging, roadworks and rest stops all reduce the average without ever showing on the speedometer. Planners typically assume a door-to-door average of about eighty-five per cent of the posted limit on open roads.
- What is the difference between speed and velocity?
- Speed is a scalar: it has size only. Velocity is a vector with both size and direction. A car that drives a full lap of a circuit at 100 km/h has a high average speed but an average velocity of zero, because it finishes exactly where it started. This calculator works entirely with speed.
- How do I turn a race time into a pace?
- Solve for speed using the race distance and your target time, then read the pace per kilometre or per mile in the results. A 3 hour 30 minute marathon needs about 4:59 per kilometre or 8:01 per mile. Training at that exact pace is what makes it sustainable on race day.
- What is a knot and why do boats and aircraft use it?
- A knot is one nautical mile per hour, and a nautical mile is 1,852 metres, which is very close to one minute of latitude. That makes navigation on a chart simple, because a distance measured against the latitude scale converts directly into time at a known speed. One knot is 1.852 km/h.
- Does this work for acceleration problems?
- Only partly. For constant acceleration from rest the average speed is half the final speed, so you can enter that average here to get the distance or the time. Anything involving changing acceleration needs the full kinematic equations rather than the simple speed triangle this calculator solves.
Use this with
Speed Distance Time Calculator answers one part of the question. These pick up where it stops: Running Pace Calculator, Fuel Cost Calculator, Road Trip Planner Calculator and Fuel Efficiency Calculator.
Where these figures come from
This calculation is jurisdiction-neutral arithmetic. No country-specific rules are applied.
- NIST Special Publication 811: Guide for the Use of the SI. Exact conversion factors and correct unit style
- BIPM: The International System of Units (SI Brochure). The defining text for the SI
Speed Distance Time Calculator produces an estimate for general information. It is not financial, tax, medical, legal or engineering advice. read the full disclaimer. Spotted a wrong number? Report it and it gets fixed. The form picks up this calculator and the inputs you used.