Current versions of Arduino IDE

Use the menu option in the Arduino IDE:

Sketch ► Export Compiled Binary

See post #6 from the thread How to get hex file from arduino files ?:

Well, since it was bumped it's worth mentioning there is a new way to
do this added in Arduino IDE 1.6.5:

• Sketch > Export Compiled Binary


• If you are doing this with an example then you will be prompted to save the sketch in another location.


• Wait until the sketch has finished compiling.


• Sketch > Show Sketch Folder


• The .hex file will be in the sketch folder

Here is a screenshot for OS X:

There is no need to fully compile, a simple verify will suffice. From post #10:

Reopen Arduino, and open a sketch of your choice (use the Examples->Digital->Blink if you have no other sketches). Hit the Verify button to compile the sketch. Now, navigate to the build.path folder. You should see a bunch of files including one with a .hex extension.

Older versions of Arduino IDE

If using an older version of the Arduino IDE, from post #12:

Try this if using an older version of Arduino

Taking out HEX file from Arduino in 3 simple steps

1. Open Arduino IDE


2. File ► Preferences menu

3. Find "Show verbose output during " and check the "compilation" box


4. Locate the preferences.txt file and open it



5. Add the following line (this is the path to the directory where the hexfile will be stored):

   
   
   

   build.path=C:\Users\<username>\Desktop\hexfile
   




6. Change the following line

   
   
   

   export.delete_target_folder=true
   

   
   
   

   to

   
   
   

   export.delete_target_folder=false
   




7. Quit the Arduino IDE and restart it.



8. Now when you compile, the directory specified in build.path will contain the .hex file (along with other files which can be ignored)