What’s the Minimum Java Heap Size to Run an App?

If you really want to minimize the heap size, you could strip down your app for a no-dependency configuration. For example, if you have a super basic app like this:
```java
public final class Example {
static void main() {}
}
```
And run it in a lightly configured JVM set to interpret mode, you might find you can get away with using less memory, although you’ll still have to manage whatever minimum is set by the JVM.

I ran a test with a basic "Hello World" program using Java 26 on my Mac. The absolute minimum `-Xmx` you can set is 2m, but if you try to go below that, the JVM just won't start. Interestingly, even when you set `-Xmx2m` and `-Xms2m`, the JVM actually allocates about 8 MiB for the heap due to its internal rounding. The Hello World program only uses around 1.8 MiB total, which includes class metadata and other internals, leaving quite a bit of heap unused.

For a simple test, I recommend starting your app with a 1 MB heap and gradually increase it until you find a size that works without crashing or triggering problems during initialization. This can give you a practical sense of how much memory your specific app requires.

The minimum heap size really depends on what the Java application does. If you have a simple main method, it might require less memory compared to running a server application like Apache Tomcat, which can be much more memory-intensive.

Back in the J2ME days, we had devices with only 64kb of RAM, and even 2 MB felt spacious. Those implementations included most JVM features like safe memory and garbage collection, but the current Java runtime's API size limits how much you can shrink things down now.