Speed Distance Time Calculator
Solve for speed, distance, or time when you know the other two — enter any two of the three values and this calculator computes the third using the d = s
Speed Distance Time Calculator
Calculator
Adjust values & calculateEnter your values below. Every result is computed in your browser — no data is sent to any server.
Formula: Speed = Distance / Time | Distance = Speed × Time | Time = Distance / Speed
Worked example — 2.5 hours
Formula
Speed = Distance / Time | Distance = Speed × Time | Time = Distance / Speed
Enter any two values to calculate the third. Leave one field empty to solve for it.
Worked Examples
Example 1: Road trip
Problem:60 mph for 150 miles
Solution:Time = 150/60 = 2.5 hours
Result:2.5 hours
Example 2: Solving for required speed
Problem:You need to cover 240 km and have exactly 3 hours available before an appointment. What average speed do you need to maintain?
Solution:Speed = Distance / Time = 240 km / 3 hours
Result:80 km/h required average speed
Frequently Asked Questions
How do I convert between speed units?
mph × 1.609 = km/h. km/h ÷ 3.6 = m/s. mph × 0.447 = m/s.
How do I calculate average speed for a trip with multiple segments?
Average speed is total distance divided by total time, NOT the arithmetic average of segment speeds. For example, driving 60 mph for 2 hours and then 30 mph for 1 hour gives average speed = 150 miles / 3 hours = 50 mph, not the arithmetic mean (60+30)/2 = 45 mph. However, if each segment covers equal distance (not time), the harmonic mean applies: 2/(1/60 + 1/30) = 40 mph.
What is the stopping distance at different speeds?
Stopping distance = thinking distance + braking distance. At 30 mph: ~23 m total. At 60 mph: ~73 m total. At 70 mph: ~96 m total. Braking distance increases with the square of speed, so doubling speed quadruples braking distance. Wet roads roughly double the braking distance, and reaction time is typically 0.7-1.0 seconds for alert drivers.
How is pace (min/km or min/mile) different from speed?
Speed is distance per unit time (e.g., 10 km/h), while pace is the inverse: time per unit distance (e.g., 6 min/km). Runners typically use pace because it directly tells you how long each kilometer or mile will take. To convert: pace (min/km) = 60 / speed (km/h). A 5-minute mile pace equals 12 mph or 19.3 km/h.
Which of the three variables should I leave blank?
Leave blank whichever value you don't know and want to solve for — the calculator works algebraically in any direction. If you know how far you traveled and how long it took, leave Speed blank to find your average speed. If you know your speed and the distance, leave Time blank to find how long the trip will take. If you know your speed and how much time you have available, leave Distance blank to find how far you can go. Entering all three values is unnecessary since two variables always determine the third under the d = s × t relationship.
Why does my calculated speed differ from a GPS or speedometer reading?
Speed Distance Time Calculator returns average speed over the full distance and time entered, while a speedometer or GPS shows instantaneous speed at a single moment. A trip that includes stoplights, traffic, or rest breaks will always show a lower average speed than the peak speed reached on the open road. For example, a 100-mile trip completed in 2 hours has an average speed of 50 mph even if you spent part of the trip at 70 mph and part of it stopped at a red light — the two effects cancel out in the total-distance-over-total-time calculation.
What is the difference between speed and velocity in this calculation?
Speed is a scalar quantity with magnitude only, while velocity is a vector that also carries direction. Speed Distance Time Calculator uses speed, so the distance you enter should be the total path length travelled rather than straight-line displacement. Drive a 40 km loop and return to your starting point in one hour and your average speed is 40 km/h, but your average velocity is zero because net displacement is zero. The distinction matters in physics problems, where vector kinematics tracks displacement instead of path length.
Does the d = s x t formula still work when the vehicle is accelerating?
The formula d = s x t assumes constant speed, so with acceleration it only returns the average speed over the interval, not the speed at any given instant. For uniformly accelerated motion, use the kinematic equations instead: d = ut + 0.5at squared, and average speed = (u + v) / 2 where u is initial and v is final speed. A car accelerating evenly from 0 to 60 mph averages 30 mph, so it covers half the distance a steady 60 mph would.
Why must the distance unit match the speed unit I select?
The relationship d = s x t is only dimensionally consistent when the length unit in the speed matches the length unit of the distance. Entering 100 for distance in kilometres while selecting mph makes the calculator treat those kilometres as miles, inflating or deflating the answer by the 1.609 conversion factor. Convert first: divide kilometres by 1.609 to get miles, or multiply miles by 1.609 to get kilometres. Time is always entered in hours here, so m/s inputs need converting as well.
How do I enter a time given in minutes and seconds?
Convert it to decimal hours before entering it, because the Time field is read as hours. Divide minutes by 60 and seconds by 3600, then add them: 1 hour 45 minutes becomes 1 + 45/60 = 1.75, and 2 minutes 30 seconds becomes 2/60 + 30/3600 = 0.04167. A common error is typing 1.45 for one hour forty-five minutes, which the calculator reads as 1 hour 27 minutes and skews the solved distance by roughly 17 percent and the solved speed by about 21 percent — close to a fifth either way.
References
Reviewed for accuracy by Daniel Agrici, Founder & Lead Developer · Editorial policy
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