How many stamps are needed to mail a manilla envelope with 3 papers inside?

The number of stamps needed to mail a manila envelope with three papers inside depends on the total weight and the mailing service you choose. Generally, for a standard letter under 1 ounce, you would need one first-class stamp. If the envelope exceeds that weight or requires additional services, you may need to add more stamps. It's best to check with your local postal service for specific weight limits and rates.