Model size in GB = VRAM required for uncompressed inference (16bit aka "half precision) plus ~1-4GB for context. For 8bit you need half that. For GPTQ/4bit you need 1/4 that.

For example, assuming GPTQ 4bit a 100GB 16bit model needs 26-30GB of VRAM. The smallest video cards which meet this requirement will be 32GB or 40GB cards. (two 24GB cards in parallel work as well, e.g. 2x3090)

You want the entire model to fit in memory. So if you’re looking at a download size of, say, 100GB then don’t run on less than that. Your machine will swap to/from disk constantly, which will be slow and wear out an SSD.

If you want to train a model, that’s a different story.