Hey guys I have build a 450 sized quad which weighs about 1kg I am using a2212 1400 kv motors with 30 amp esc's. I am confused about  what prop to use  . Plz help.
Regards

It depends on thrust.
Small size propeller used in higher kv motor and large size used in lower kv motor.
You can try small propeller
watch this

The maximum size of prop a 1400kv motor can take on a 3cell LiPo is 7-8". (Current draw would be around 15-17A)

From the data sheet, 8x4 looks like a good choice.

Ordered 8*4.5 as 8*4 props weren't available.

It depends on the max current that motor can handle. I had a 1400kv 3S setup with 1045 prop but the max motor current was within 20A.