Speed Distance Time Calculator
Physics & EngineeringSolve for speed, distance, or time using the classic distance equals speed times time formula. Free calculator with mph, km/h, mile, and km unit toggles.
Average Speed
The average speed over the trip.
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Odeh Ahwal0people find this calculator helpful
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Physics & Engineering calculators
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Odeh Ahwal0people find this calculator helpful
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Physics & Engineering calculators
This calculator solves any one of speed, distance, or time once you know the other two. Pick which value you want to find from the Solve For menu, enter the two values you already have, and it computes the third instantly, with results also shown in hours and minutes when solving for time.
All three versions come from the same underlying relationship: distance equals speed multiplied by time. Rearranging that one formula gives you all three directions, so speed equals distance divided by time, and time equals distance divided by speed.
One honest note on terminology: this calculates average speed over the whole trip, not your instantaneous speed at any single moment, and not velocity, which also accounts for direction. If your actual speed varied along the way, a constant speed covering the same distance in the same time is mathematically equivalent, even though it does not describe what really happened moment to moment.
The Distance, Speed, and Time Formula
The core relationship is distance = speed times time. Rearranging it algebraically gives the other two versions you need, depending on which value is unknown.
| To Find | Formula |
|---|---|
| Speed | Speed = Distance / Time |
| Distance | Distance = Speed x Time |
| Time | Time = Distance / Speed |
The Distance-Speed-Time Triangle
A common memory aid puts Distance on top of a triangle, with Speed and Time on the bottom two corners. Cover up whichever value you want to find: if you cover Distance, Speed and Time are left side by side, meaning you multiply them. If you cover Speed or Time, the remaining value sits over the other, meaning you divide.
Average Speed vs Average Velocity
Speed and velocity are often used interchangeably in everyday conversation, but they mean different things in physics. Speed is a scalar quantity, just a number and a unit, like 60 mph. Velocity is a vector quantity, meaning it also has a direction, like 60 mph due north.
The difference matters most on a round trip. If you drive 100 miles out and 100 miles back, your average speed for the whole trip is a real, positive number based on the total distance traveled. Your average velocity, however, is zero, since your net displacement, how far you ended up from where you started, is zero. This calculator computes average speed, the total-distance version, not velocity.
Worked Examples for Each Formula
Here is the same 150 mile, 60 mph, 2.5 hour trip solved three different ways, one for each variable.
| To Find | Known Values | Calculation | Result |
|---|---|---|---|
| Speed | 150 mi, 2.5 hr | 150 / 2.5 | 60 mph |
| Distance | 60 mph, 2.5 hr | 60 x 2.5 | 150 mi |
| Time | 150 mi, 60 mph | 150 / 60 | 2.5 hr (2h 30m) |
Frequently Asked Questions
How do I calculate average speed?
Average Speed = Total Distance / Total Time. This gives the overall average, not your instantaneous speed at any single moment during the trip.
How do I calculate distance if I know speed and time?
Distance = Speed times Time. For example, traveling at 60 mph for 2.5 hours covers 60 times 2.5, which is 150 miles.
How do I calculate time if I know distance and speed?
Time = Distance / Speed. For example, covering 150 miles at 60 mph takes 150 divided by 60, which is 2.5 hours, or 2 hours and 30 minutes.
What is the distance-speed-time triangle?
It is a memory aid with Distance on top and Speed and Time on the bottom two corners. Covering the value you want to find shows whether to multiply or divide the other two to get it.
What is the difference between average speed and average velocity?
Average speed is total distance divided by total time and is always a positive number. Average velocity is total displacement, the straight-line distance from start to end, divided by time, and can be zero or negative depending on direction, even on a trip with real average speed.
What is the difference between average speed and instantaneous speed?
Average speed covers an entire trip or time period. Instantaneous speed is the reading at one specific moment, like a speedometer needle at a single instant, and can be higher or lower than the average at different points along the way.
What is the symbol for speed?
Speed is usually written as v in physics, the same letter used for velocity, since the formulas for their magnitude are the same. Distance is usually d or s, and time is t.
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