It has been scientifically proven that there are 86,400 seconds in 1 day.
This is the mathematical equation used to solve this question:
60 x 60 x 24 = 86,400
The first 60 represents 60 seconds which is equal to 1 minute.
The second 60 represents 60 minutes which is equal to 1 hour.
The 24 represents 24 hours which is equal to 1 day.
Therefore - 60 (seconds) x 60 (minutes) x 24 (hours) = 86,400 (seconds in 1 day)
However if it's a leap year, where there is an additional day all you need to do is take the already established 86,400 (seconds in 1 day) and estimate it to the nearest 24 (hours) and you will get the following answer: 86,163.934 (seconds in 1 day).