Decimal to H:MM: 7.5 becomes 7:30
7.5 decimal hours splits into 7 whole hours, plus 0.5 of an hour remaining. Multiplying that 0.5 by 60 gives 30 minutes — so 7.5 decimal hours is 7 hours 30 minutes, written 7:30.
H:MM to decimal: 0:45 becomes 0.75
Going the other direction, 45 minutes divided by 60 gives 0.75 — so 0 hours 45 minutes is 0.75 decimal hours. The calculator detects which direction to convert automatically by checking whether the entered value contains a colon.
Why payroll systems need the decimal form
A hidden reason this conversion matters: multiplying hours by an hourly wage rate only works cleanly with decimal hours. "7 hours 30 minutes × wage rate" isn't a valid multiplication until the 30 minutes is expressed as 0.5 of an hour — decimal hours exist specifically to make that multiplication straightforward.
Where this conversion's inputs actually come from
In practice, the H:MM figure being converted is usually itself the output of another calculation — like the duration of a work shift — rather than typed in directly. The companion article on calculating a shift's duration shows exactly that starting point.