The NOAA Unit Converter for Oil Spills (NUCOS) is a simple desktop tool that converts basic units of velocity, mass, length, etc., but more specifically, converts units that are unique to oil spill response.

NUCOS includes some of the lesser known units used in managing oil and chemical spills. For example, it converts the units for oil volume, viscosity, and density from the conversion list of the Estimated Dispersant System Potential calculator (EDSP), a tool that helps spill responders assess dispersant application system performance. Additionally, it converts API gravity, oil surface concentration, and latitude and longitude formats.

NUCOS is compatible with Windows 7 and greater, and Mac OS-X versions 10.13 and greater. The Mac installer was designed for Intel-based Macs, but will also run on newer Macs that use Apple's M-series chips. Installation of NUCOS includes a short Help file.

NUCOS was developed by NOAA's Office of Response and Restoration (OR&R). The current version, NUCOS 4.2.1, was posted on August 5, 2025. Version 4.2.1 includes more conversion units than the original version.

View of an oil quantity conversion in the unit converter, NUCOS. Image credit: NOAA.

To download NUCOS, click on the appropriate download link:

• NUCOS for Windows [Windows Executable, 14.2 MB]
• NUCOS for Mac [Mac Disk Image, 20 MB]

On a Windows PC: Double-click the "Nucos4.2.1Installer.exe" file icon, then follow the directions you'll see on your screen.

On a Mac: Double-click the disk image file "NUCOS-4.2.1.dmg" to open it. You should now see the NUCOS file icon. (You can move the NUCOS file icon to wherever you would like NUCOS to reside. We suggest the "Applications" folder.)

In Windows: To start NUCOS, from the Start menu, under Programs, choose "NUCOS."

On a Mac: To start NUCOS, double-click the NUCOS file icon.

Questions: Contact us with your questions, comments, or suggestions for NUCOS.