Speed Distance Time Calculator
Pick what you want to find, enter the other two values, and get an instant result.
The Speed Formula
Speed = distance ÷ time.
The formula is literally derived from d = rt (distance = rate × time) — this calculator just solves it for whichever variable you're missing. Rearranged, distance = speed × time, and time = distance ÷ speed.
Worked example
A trip covers 150 miles in 2.5 hours.
150 ÷ 2.5 = 60
Speed: 60 mph
A second example, a genuinely tricky one: a round trip driven at 60 mph going and 40 mph returning over the same distance. What's the average speed for the whole trip?
It's not the simple average, (60 + 40) ÷ 2 = 50 mph. Since more time is spent at the slower speed, the true average is the harmonic mean: 2 × 60 × 40 ÷ (60 + 40) = 4,800 ÷ 100.
Average speed: 48 mph
Common mistake
Mixing units is the most common error — plugging minutes into a formula that expects hours. 45 minutes must first convert to 0.75 hours (or the speed must convert to miles per minute) before multiplying by a speed given in miles per hour.
Keep going
- Speed, distance, and time relate through direct proportion; the proportion calculator solves that same kind of a/b = c/x relationship in general form. Proportion Calculator
- Speed calculations only work cleanly when the units match; the mph to kmh calculator converts a speed before it goes into a distance or time problem. MPH ↔ KM/H Calculator
Frequently Asked Questions
What is the speed, distance, time formula?
Speed = distance ÷ time. Rearranged, distance = speed × time, and time = distance ÷ speed.
How do you find average speed for a trip with different speeds?
Average speed is total distance divided by total time, not a simple average of the individual speeds — this matters most when the same speeds are held for different amounts of time.
What units should I use?
Any units work as long as they're consistent — miles and hours, kilometers and hours, or meters and seconds all give a valid speed, as long as distance and time use matching units.
How do you find distance when you know speed and time?
Rearrange the formula: distance = speed × time. A cyclist riding at 12 mph for 45 minutes (0.75 hours) covers 12 × 0.75 = 9 miles.
Why isn't a round trip's average speed just the average of the two speeds?
Because average speed is total distance divided by total time, and the trip spends more time at the slower speed. A driver going 60 mph one way and returning the same distance at 40 mph doesn't average 50 mph — see the worked example below.
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