How much concrete mix or number of 20kg bags is required to cover an area of 2m long x 150mm deep x 400mm wide.
Here is a link for a concrete calculator that will do that for you, hope it helps
Welcome to the Bunnings Workshop community @PeteB8. It's sensational that you've joined us, and many thanks for your question about the number of concrete mix bags you'll need for your slab.
I apologise as I read your measurements incorrectly. I've now edited my response below to reflect the correct amount.
We look forward to hearing more about your concrete slab project. Please let us know if you have further questions or need assistance.