Every LLM inference engineer hits this wall eventually.

You deployed a model, it works in testing, then production traffic arrives. Suddenly your 80GB A100 is OOM on a 70B model that "should fit."

The culprit is almost always the KV Cache. But most discussions stop at "it caches the Key and Value matrices" — which doesn't help you predict when you'll run out of memory.

This post gives you a quick estimator formula, explains when to worry, and what levers actually help.

The One-Number Formula