Days to Seconds
Type a value in either box to convert between days and seconds. The factor is 86400.
| Days | Seconds |
|---|---|
| 1 day | 86400 s |
| 2 day | 172800 s |
| 3 day | 259200 s |
| 5 day | 432000 s |
| 10 day | 864000 s |
| 25 day | 2160000 s |
| 50 day | 4320000 s |
| 100 day | 8640000 s |
How to use
- Enter a value in the Days field.
- The Seconds figure appears immediately — no button to press.
- Typing in the Seconds field converts back to Days the same way.
- Use the reference table for the values that come up most often.
Days to Seconds formula
Converting days to seconds is a single multiplication by 86400.
s = day × 86400
Put another way, one day is exactly 86,400 seconds.
Why this factor: the day and the second are both defined against the second, so dividing one definition by the other gives 86400 directly. Both definitions are set out in full below.
To go the other way, divide by 86400 — or use the Seconds to Days converter, which is the same calculation reversed.
Worked example
Start with 90 day. Multiply by 86400 to get 7776000 s.
90 day × 86400 = 7776000 s
The converter above does this for any value you type, in either direction.
What is a day?
A day is 24 hours, one nominal rotation of the Earth.
Definition: Exactly 86,400 seconds by convention. The Earth's actual rotation drifts slightly, which is what leap seconds correct.
Where it is used: Calendars, project schedules, hotel and rental periods, and interest accrual.
What is a second?
The second is the SI base unit of time and the most precisely realized unit in all of measurement.
Definition: Defined by fixing the caesium-133 hyperfine transition frequency at exactly 9,192,631,770 hertz — the basis of every atomic clock.
Where it is used: Universal, and the reference for all other time units.
Days vs Seconds
The day is a specialized unit while the second is an SI unit. That is why the factor between them is not a round number: the two systems were defined independently and only later tied together by exact agreement.
Frequently asked questions
How many seconds are in a day?
One day equals 86400 seconds.
What is the formula to convert days to seconds?
Multiply the number of days by 86400. To reverse it, divide by 86400 instead.
How do I convert seconds back to days?
Divide by 86400, which is the same as multiplying by 1.15740741e-05.
How many seconds are in 10 days?
10 day works out to 864000 s.
How is the day defined?
Exactly 86,400 seconds by convention. The Earth's actual rotation drifts slightly, which is what leap seconds correct.