How do I increase the heap space for the Java VM in MATLAB?
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How do I increase the heap space for the Java VM in MATLAB?
Accepted Answer
MathWorks Support Team
on 10 Sep 2025
Edited: MathWorks Support Team
on 10 Sep 2025
For MATLAB R2010a onwards:
You can change this setting using the Preferences dialog box. For more information, refer to the documentation page on 'Java Heap Memory Preferences'.
This can also be accessed as follows:
1. Open the help browser by typing at the MATLAB Command Window:
>> doc
2. Search for 'Java Heap Memory Preferences' on the search bar of this documentation browser.
For MATLAB R2009b and earlier:
You can increase the heap space for the Java Virtual machine (VM) by using the following file:
java.opts
Please follow the instructions below:
1. Create 'java.opts' file:
Create a text file named 'java.opts' in the $MATLABROOT/bin/$ARCH directory. $MATLABROOT is the MATLAB root directory and $ARCH is your system architecture, which you find by typing at the MATLAB Command Window:
>> matlabroot
>> computer('arch')
If you do not have write-access to $MATLABROOT/bin/$ARCH, or if you want a user-specific version, create the 'java.opts' file in the MATLAB startup directory. The MATLAB startup directory can be found by executing the following at the MATLAB Command Window (before any MATLAB code is executed):
>> pwd
If you use MATLAB 7.7 (R2008b) or later versions on a MAC OS system, MATLAB default installation directory is
/Applications/MATLAB_<Release>.app
where '<Release>' is the MATLAB Release's version, i.e., R2008b, R2009a, etc. To access the contents of the /Applications/MATLAB_<Release>.app directory, in Finder, navigate to Applications and right-click on 'MATLAB_<Release>.app'. Click 'Show Package Contents' and you will be able to see the contents of the directory.
2. Determine the version of the Java Virtual Machine (JVM) in use:
The contents of 'java.opts' depend on your version of the JVM. To determine the version of the JVM you are running, type the following at the MATLAB Command Window:
>> version -java
NOTE: If you are performing these operations in MATLAB 7.5 (R2007b), read this bug report:
3. Determine the value to put in the 'java.opts' file:
When MATLAB is launched, it starts up the Java Runtime Environment. MATLAB uses a set of default values for the initial and maximum heap size (managed by the heap manager). When the free memory nears zero, Java will dynamically increase the heap size (up to the Max Heap Size setting). The following table shows the default settings MATLAB uses for versions of the JVM:
JVM Initial Heap Size Max Heap Size
1.6.0 -Xms64m -Xmx128m (32-bit)
-Xmx196m (64-bit)
1.5.0 -Xms64m -Xmx96m (32-bit)
-Xmx128m (64-bit)
1.4.2 -Xms16m -Xmx96m
1.3.1 -Xms16000000 -Xmx64000000
1.2.2 -Xms16000000 -Xmx64000000
1.1.8 -ms16000000 -mx64000000
You can use the following commands to obtain information about the Java heap space usage in MATLAB:
>> java.lang.Runtime.getRuntime.maxMemory
>> java.lang.Runtime.getRuntime.totalMemory
>> java.lang.Runtime.getRuntime.freeMemory
Users can override these values by setting them manually in a 'java.opts' file. For example, including the following line in a 'java.opts' file sets the Max Heap Size value to 256 MB:
For JVM of 1.2.2 and later, place the following in your 'java.opts' file:
-Xmx256m
For JVM 1.1.8 'java.opts', place the following in your 'java.opts' file:
-mx256m
This will give you 256MB of JVM memory and you can adjust the parameter as needed. Remember that increasing the size of the Java heap may correspondingly decrease the amount of space available for MATLAB arrays. For more information, refer the following guide on Memory Management:
4. Troubleshooting:
In some cases, increasing the Java heap size above a certain limit can cause Java memory problems. See this solution for more information:
If you are increasing the Java heap size in response to an 'OutOfMemoryError: Java heap space', and you get the same error with the larger heap, you may have a memory leak, or you may be retaining references to Java objects beyond their usefulness. The Java SE Troubleshooting guide may help isolate the problem:
1 Comment
sudobash
on 6 Jun 2025
This link seems useful: https://in.mathworks.com/support/bugreports/398525
More Answers (1)
Igor Varfolomeev
on 19 Jun 2015
Edited: MathWorks Support Team
on 20 Jun 2025
Although the Answer by MathWorks Support Team is correct for old matlab versions, here's a cople of notes, concerning more recent versions:
-------
1. First of all, now "Max Java Heap Memory" parameter could be changed via a slider in Preferences->Matlab->General->Java Heap Memory
2. If the maximum value, allowed by this slider, is too small for your needs, (e.g. R2014b only allows me to set it to 49GB, while physically I have 192GB), it could be directly adjusted by editing
"c:\Users\%USERNAME%\AppData\Roaming\MathWorks\MATLAB\R2014b\matlab.prf"
3. Open it with a text editor and modify "JavaMemHeapMax" value. It should look like
JavaMemHeapMax=I190000
4. Restart Matlab
-------
Notes:
- Since this preferences file is in your AppData folder, you even don't need administrative permissions (in contrast to adding "java.opts" to $MATLABROOT, as discussed in the mentioned answer.
- To check the actual value, used by Matlab (in GB):
>> java.lang.Runtime.getRuntime.maxMemory/1e9
- Preferences UI works OK with this new value (thanks, Mathwoks!). It just displays a warning, that it is larger, then recommended.
4 Comments
K E
on 15 Feb 2016
Edited: MathWorks Support Team
on 24 Jun 2021
Here is how to find out your machine's max heap size (returns values in bytes while JavaMemHeapMax looks for value in MB). Should I use this value for the Matlab preference above? Why did you enter JavaMemHeapMax=I190000 when you said you had 192GB? Even after I entered my max value of 4GB and it 'took' in Matlab, exporting a figure from the figure window Edit button causes Matlab to freeze for several minutes then issue the error 'Insufficient Java memory to create the output. Increase the Java Heap Size setting in the MATLAB preferences.' I am plotting 2052075 points within the figure. Is 4GB too low to copy that? Didn't see this problem until R2015b.
Namita Vishnubhotla
on 22 Apr 2016
Edited: MathWorks Support Team
on 27 Apr 2023
It is possible that the output requires more than 4GB. If you were able to successfully execute the same code in previous versions of MATLAB, using the same amount of Heap Space, please contact MathWorks Technical Support with valid license number: https://www.mathworks.com/support/contact_us.html?s_tid=contact_us_support_cust_serv
Vandana Ravichandran
on 22 Feb 2017
Edited: Vandana Ravichandran
on 22 Feb 2017
This page from R2016b documentation describes how to set the Java heap space: https://www.mathworks.com/help/matlab/matlab_external/java-heap-memory-preferences.html
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