270x160x20mm royal mail

A package size!

According to Royal Mail's size and weight limits, a package with the dimensions you provided:

• Length: 270mm
• Width: 160mm
• Height: 20mm

falls into their Large Letter or Small Parcel category. Here are the relevant details:

• Large Letter: Up to 245mm x 180mm x 20mm (max weight 100g)
• Small Parcel: 245mm x 180mm x 20mm to 610mm x 460mm x 460mm (max weight 2kg)

Since your package exceeds the maximum length and width of a Large Letter, but is within the maximum height, it would be classified as a Small Parcel.

For pricing and delivery estimates, you can use Royal Mail's online calculator or consult their website for more information. Keep in mind that the actual cost and delivery time may vary depending on the service you choose (e.g., 1st Class, 2nd Class, Signed For, etc.) and the destination.