A day is 86,400 seconds.
Days to Seconds Converter — d to s
Convert Days (d) to Seconds (s) using the exact conversion factor (1 days = 86,400 seconds). See the formula, worked examples, conversion table, unit comparison, history, and common uses.
Days to Seconds converter
Converter
Astronomy Converter
Convert astronomical length, mass, time, and distance units by compatible family.
Context values
Some unit families need one extra value for a physically accurate result.
The second is the SI base unit of time.
Result = input x 86400 / 1.
Time units are compatible.
Reserved above the conversion cards and below the converter.
About Converting Days to Seconds
Days and Seconds both describe astronomical distances at very different scales — one for measuring within our solar system, the other for the distances between stars — and converting between them helps put the scale of space into perspective. Days is most often used for calendars and scheduling worldwide.
Formula
seconds = days × 86400
This factor comes from each unit's defined relationship to the category's base unit: 1 days equals 86400 base units, and 1 seconds equals 1 base unit, so dividing one by the other gives the direct days-to-seconds factor of 86400.
Simple example
1 d × 86400 = 86,400 s
1 days = 86,400 seconds.
Real-world example
4.24 d × 86400 = 366,336 s
4.24 days = 366,336 seconds.
Conversion table
| Days (d) | Seconds (s) |
|---|---|
| 1 d | 86,400 s |
| 4.24 d | 366,336 s |
| 10 d | 864,000 s |
| 100 d | 8,640,000 s |
| 1,000 d | 86,400,000 s |
| 1,000,000 d | 86,400,000,000 s |
Reverse conversion: Seconds to Days
1 s × 0.00001157407407 = 0.0000115741 d
1 seconds = 0.0000115741 days.
days = seconds × 0.0000115740740741
For a page dedicated to this direction, see Seconds to Days.
Days vs. Seconds
| Aspect | Days | Seconds |
|---|---|---|
| Family | Non-SI unit accepted for use with SI | SI base unit |
| Typical use | Calendars and scheduling worldwide | Fundamental unit for all timekeeping and scientific measurement |
| Where it's used | Universal | Universal |
Understanding the Days
Days (d) measures time. A day is defined as exactly 86,400 seconds (24 hours), approximating one rotation of the Earth. It is classified as a Non-SI unit accepted for use with SI.
Where it's used: Universal
Uses of the Days today
- Calendars and scheduling worldwide
- Age, tenure, and duration calculations
- Project planning and deadlines
History of the Days
The day as a natural unit (one Earth rotation) is prehistoric in origin; its fixed 86,400-second definition follows from the standardized hour, minute, and second, decoupling the calendar day slightly from the actual (very gradually lengthening) astronomical day.
Historical origin. Days was not the invention of a single named person; it developed through the process described above.
Understanding the Seconds
Seconds (s) measures time. The second is the SI base unit of time, currently defined via a fixed number of cesium atomic transitions. It is classified as a SI base unit.
Where it's used: Universal
Uses of the Seconds today
- Fundamental unit for all timekeeping and scientific measurement
- Basis for derived units like speed (m/s) and frequency (Hz)
History of the Seconds
The second originated from dividing the day into 24 hours, each into 60 minutes, each into 60 seconds — a sexagesimal (base-60) system inherited from Babylonian astronomy. Since 1967, the second has been defined atomically, as exactly 9,192,631,770 periods of radiation from a cesium-133 transition, decoupling timekeeping from the Earth's slightly irregular rotation.
Historical origin. Seconds was not the invention of a single named person; it developed through the process described above.
Days — sources
- BIPM SI Brochure — Non-SI units accepted for use with SI — Lists the day among accepted non-SI time units.
Seconds — sources
- BIPM — The second (SI base unit) — Current atomic definition and history of the second.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many seconds are in 1 days?
1 days equals 86,400 seconds, using the exact defined conversion factor rather than an estimate.
How do I convert days to seconds?
Multiply the days value by 86400. The converter above does this instantly to whatever precision you set.
How do I convert seconds back to days?
Use the reverse factor: 1 seconds equals 0.0000115741 days. You can also use the swap control in the converter above to flip the direction instantly.
What is a days?
Days (d) measures time. A day is defined as exactly 86,400 seconds (24 hours), approximating one rotation of the Earth. It is classified as a Non-SI unit accepted for use with SI.
What is a seconds?
Seconds (s) measures time. The second is the SI base unit of time, currently defined via a fixed number of cesium atomic transitions. It is classified as a SI base unit.
Is the days to seconds conversion exact?
Yes. A day is defined as exactly 86,400 seconds (24 hours), approximating one rotation of the Earth. That fixed definition is what the converter above uses, so any rounding you see is a display choice, not a limitation of the math.
Where is the days still used today?
Universal