Featured article photo: Singapore HDB by Andrew Haha Lee
The majority of offices as well as housing in Singapore are in high-rise buildings (e.g. HDBs, apartments, condominiums), and they all share the same address format.
[Block Number] [Street Name] #[Unit Level]-[Unit Number] [Building Name] Singapore [Postal Code]
(Side note: If you are unsure what an HDB is, it is a public housing unit by the Government of Singapore.)
The following example refers to a unit located on 101 Marlow Street in the Clife Building, at level 12 with unit number 05 (all example addresses in this post are dummy addresses):
101 Marlow Street
#12-05 Clife Parkview
Note that Singapore uses a 6-digit-number postal code.
From my personal experience, omitting a building name will typically not have a major impact in mail deliverability. Some HDBs might not have a building name, and it is acceptable to format the address as follows:
101 Marlow Street #12-05
For landed properties, because there is no unit level, unit number, and building name, the second line from the address format above can be omitted completely:
[Unit Number] [Street Name] Singapore [Postal Code]
60 Aria Street