These calculators are almost entirely useless. They don't understand specific model architectures. Even the ones that try to support only specific models (like the apxml one) get it very wrong a lot of the time.

For example, the one you linked, when I provide a Qwen3.5 27B Q_4_M GGUF [0], says that it will require 338 GB of memory with 16-bit kv cache. That is wrong by over an order of magnitude.

[0] https://huggingface.co/bartowski/Qwen_Qwen3.5-27B-GGUF/resol...