A worked example: 5000 seconds
Feeding 5000 seconds into the seconds calculator's formula returns 1 hour, 23 minutes, and 20 seconds, alongside decimal totals of 83.3333 total minutes and 1.3889 total hours. The h:m:s breakdown and the decimal totals describe the same duration in two different shapes — one for reading, one for comparing.
The formula: floor division and modulo, in that order
Hours come from floor(seconds ÷ 3600): floor(5000 ÷ 3600) = 1, leaving a remainder of 5000 − (1 × 3600) = 1400 seconds still to place. Minutes come from floor(that remainder ÷ 60): floor(1400 ÷ 60) = 23, using up 23 × 60 = 1380 seconds. Whatever's left over is the seconds value: 1400 − 1380 = 20. Total minutes and total hours are computed separately, straight from the original 5000 seconds (5000 ÷ 60 = 83.3333, 5000 ÷ 3600 = 1.3889), not from the rounded h:m:s pieces.
A round-number example: 9000 seconds
9000 seconds is a cleaner case: floor(9000 ÷ 3600) = 2 hours exactly, with a remainder of 9000 − 7200 = 1800 seconds. floor(1800 ÷ 60) = 30 minutes, using the remainder exactly and leaving 0 seconds. The decimal totals confirm it lines up neatly too — 9000 ÷ 60 = 150 total minutes and 9000 ÷ 3600 = 2.5 total hours, with no rounding needed either way.
Why the decimal totals still matter
The h:m:s breakdown is the easiest to read, but the decimal totals are what make two durations comparable at a glance — 1.3889 total hours versus 2.5 total hours tells you instantly that the second duration is longer, without mentally converting "1h 23m 20s" and "2h 30m 0s" into the same unit first. That's why the calculator reports both forms instead of just one.