It is normally between 14 to 30 days. Regardless of the length of stay granted, visitors may request for an extension of stay by applying in person at the Immigration and Checkpoints Authority before the expiry of the visa granted.

For more details : https://www.mfa.gov.sg/Services/Visitors/Visa-Information

For apply E-visa online : https://www.ica.gov.sg/enter-transit-depart/entering-singapore/visa_requirements