Treadmills tend to show speeds in miles per hour or kilometres per hour, whereas running watches (and runners) tend to work in minutes per mile or minutes per kilometre. Not many runners consider metres per second, although it's occasionally of interest to sprinters.
This calculator quickly converts between different running speeds and paces, and also finish times for 5k, 10k, half marathon and marathon.
Fill in any field and all the other fields will update. The conversion is automatic and instant.
You can also generate a summary of speeds/paces/finish times which, in addition to summarising the values on the page, adds some useful (and some not so useful, but possibly interesting) speed comparisons.