Speed, Distance & Time Calculator
How it works
Everything here comes from one equation: distance = speed × time. Whichever of the three fields is empty tells the calculator which one to solve for — the other two are rearranged to isolate it: speed = distance ÷ time, or time = distance ÷ speed. No units are converted anywhere in that arithmetic, so the three numbers need to already share one consistent system before you type them in.
Frequently asked questions
Why do I have to leave exactly one field blank?
One equation, distance = speed × time, can only pin down one unknown at a time. Leaving all three filled in would either be asking the tool to confirm numbers you already have (redundant) or handing it an inconsistent set with no single right answer to solve for — this tool is built to solve for one unknown, not to referee three knowns against each other.
Does this convert between units, like km to miles?
No — it treats whatever you enter as one consistent system and solves the equation directly. Speed, distance and time need to already share compatible units before you enter them: kilometres, km/h and hours together, or miles, mph and hours together. Mixing a distance in kilometres with a speed in mph will give a number, but not a meaningful one.
What is the underlying formula?
distance = speed × time. Whichever field is left blank, the calculator rearranges that same equation to solve for it: speed = distance ÷ time, or time = distance ÷ speed. It is worth keeping in mind so any result here can be sanity-checked by hand.