Hi @Darren C 

It’s the number of unique orders placed following a message (Email or SMS) within the channel’s attribution window, divided by the number of unique recipients of that message  x100 eg (100 unique orders placed / 1000 unique recipients) x 100  = 10% placed order rate.

Note though that Klaviyo’s placed order stats aren’t always reliable with respect to message performance. For example, if you have a customer recurring subscription model, the placed order rate will be inflated: those recurring subscription orders will be attributed to the message if they fall withing the attribution window whether they open or clicked on it! 

More info on attribution window here.

Regards

Andy

Thanks for helping @bluesnapper !