Building some footings for a brick plinth to support a timber wall.
I’m going to make the concrete at least 150mm deep, but there will still be about 100 – 200mm below ground level before I get to the facing bricks above ground.
So, should I just make the concrete 350 – 450mm deep, or would one or two courses of 100mm blocks laid flat be cheaper ?
I know I could probably work it out from prices of blocks, sand & gravel, etc. I just wondered if there’s an established rule of thumb.

I’d think more about which will look and work better rather than just cost.

I had 1.25 cu/m of concrete delivered this morning for £150. Done in 10 mins and a proper solid base.

The trench is 450mm deep and I’ll be be making the concrete at least 150mm thick.
I’ll be using bricks where they are visible above ground level.
It’s the bit between 150 and 450mm I’m wondering about where it is still below ground. Should I just make the concrete 450mm thick, or should I lay two courses of 100mm blocks ?

There’s about 100 440x225x100mm blocks to a cubic metre, which works out at about £66, so blocks are cheaper per volume than ready mixed concrete, although there’s mortar and time to lay them to take in to account too, as against shuttering and mixing concrete. There’s no access for a ready mix lorry.