How to Increase IntelliJ IDEA Memory Allocation to Eliminate Lag

When using IntelliJ IDEA, many developers experience occasional lag even on machines with ample RAM because the IDE’s default JVM memory limit is set very low.

The default memory cap (often 1 GB) is the root cause of the slowdown.

For example, a computer with 16 GB of RAM may only allocate 1 GB to IDEA, leading to performance issues when running large projects.

You can check the current memory usage of your project via the IDE’s memory indicator.

To resolve the issue, follow these three steps:

Step 1: Edit Custom VM Options

In the top menu choose Help → Edit Custom VM Options (this opens the custom VM options file).

-Xmx1024m    // maximum heap size (default 1 GB)
-Xms256m     // initial heap size
-XX:ReservedCodeCacheSize=128m   // code cache size
-XX:+UseG1GC

Modify the values according to your machine’s capacity, for example:

-Xmx4096m
-Xms4096m
-XX:ReservedCodeCacheSize=256m
-XX:+UseG1GC

Step 2: Invalidate Caches

After saving the file, select File → Invalidate Caches , keep the default options, confirm, and let IDEA restart.

Step 3: Restart IDEA

Once IDEA restarts, you should notice a much smoother performance.

The same configuration method works for other JetBrains products such as PyCharm, Android Studio, WebStorm, etc.

Additional JVM parameters you may adjust include:

-server (first parameter for multi‑CPU performance)
-Xms (initial heap size)
-Xmx (maximum heap size)
-XX:PermSize / -XX:MaxPermSize (permanent generation)
-XX:MaxNewSize
-XX:+AggressiveHeap
-Xss (thread stack size)
-verbose:gc (show GC info)
-Xloggc:gc.log (GC log file)
-Xmn (young generation size)
-XX:+UseParNewGC (shorten minor GC)
-XX:+UseConcMarkSweepGC (shorten major GC)

These settings are especially useful when the heap size is large and major GC pauses become noticeable.