JVM Container Memory Calculator: Heap, Direct Memory & Limits

by Logan Farrell

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Oct 29, 2026 Developer Tools

container-management jvm memory calculation performance-tuning spring cloud

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A while ago one of our Spring Cloud Gateway pods kept getting OOMKilled even though heap graphs looked fine. The culprit was direct memory: without -XX:MaxDirectMemorySize, the JVM lets direct buffers grow to roughly the size of the max heap, on top of the heap itself. So I made a small calculator for it: https://opshubs.space/tools/jvm-container-memory-calculator/ Enter the container limit and your JVM flags (MaxRAMPercentage or -Xmx, threads, metaspace, direct memory) It estimates the full foo...