Is 150dpi good enough for A4 poster printing?

I’m designing my own prints for my Etsy shop, I’ve always made sure they’re 300dpi in the past but currently I’m working on some prints that are in more of a Photoshop-heavy style.

I start off designing them at 150dpi just to make things easier on my Mac… but now that I’m happy with the designs Im not sure I can be bothered recreating them all at 300dpi

Will it be noticeable with them being posters? E.g. it’s not like people will be reading them really close up or anything

150 and 300ppi are numbers related to the resolution of the screen. It’s pixels per inch.
It can be translated to DPI - but that is only relevant for lithographic output.

If people are printing on their own inkjet printers at home on basic paper then the saturation from the paper and the ink will soak into the paper anyway.

300 ppi is a fictional number from people doing lithographic number where it was transferred from LPI in printing (LInes Per Inch) which for typical litho printing would be set at 150 for most print work.

That number was multipled by 2 for ease to make 300DPI - but in reality this should be 150x1.41
which is 210DPI

For posters and things viewed from a distance you can go lower.

For books or anything read at arms length - it’s not recommdended.

But it also depends on the content of the poster.
A persons face might look like jaggy edges - but a scene of a foggy mountain you wouldn’t notice too much.

150ppi at actual print size is optimum for standard inkjet poster prints. However, if these are high-art ‘giclee’ type prints, then you want to aim higher, 200-300. If you are enlarging the imagery in the print process, you also have to aim higher, multiplying by your enlargement factor.

It’s more about the printer you are printing them on. The printer resolution and the way the ink goes down will have just as much effect on the quality as the input resolution.