Time duration measures elapsed time between events using hierarchical units: seconds (s), minutes (min = 60 s), hours (h = 60 min = 3,600 s), days (d = 24 h = 86,400 s), weeks (w = 7 d = 604,800 s). Larger units approximate: months (mo ≈ 30 d = 2,592,000 s), years (y ≈ 365 d = 31,536,000 s). For example, 10,000 seconds equals 2.778 hours (10,000 ÷ 3,600) or 2 hours 46 minutes 40 seconds. Duration conversions differ from time-of-day calculations (which involve calendars, timezones)—durations measure intervals independent of dates.
SI base unit for time is the second, defined since 1967 by cesium-133 atomic oscillations (9,192,631,770 cycles per second). All other units derive from seconds: minute = 60 s exactly, hour = 3,600 s exactly, day = 86,400 s exactly (defined as 24 hours, though Earth rotation varies slightly). Week = 7 days exactly. Month and year are approximate for duration purposes: calendar months vary (28-31 days), years have leap days. For precise duration conversions, use exact multiples (1 day = 86,400 s); for approximate timescales (project planning), month ≈ 30 days, year ≈ 365 days suffices.
Compound time formats (3 h 25 min 15 s) improve readability over single units (12,315 s). Converting 10,000 seconds: 10,000 ÷ 3,600 = 2 hours remainder 2,800 s; 2,800 ÷ 60 = 46 minutes remainder 40 s → 2 h 46 min 40 s. For user interfaces, compound format is intuitive; for calculations, convert to single unit (total seconds) before arithmetic. Video durations display as mm:ss or hh:mm:ss. Project timelines use days or weeks. Scientific experiments use milliseconds (ms) or microseconds (μs). Choose format and precision based on context and audience.
