---
name: "nc3tonc4"
section: "1"
platform: "linux"
package: "python3-netcdf4"
version: "1.7.2-1+b4"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/nc3tonc4"
---

# nc3tonc4(1)

a program to convert netCDF 3 files to netCDF 4 format files

## NAME

nc3tonc4 - a program to convert netCDF 3 files to netCDF 4 format files

## SYNOPSIS

**nc3tonc4** \[**-h**\] \[**-o**\] \[**--vars=*var1,var2,..***\] \[**--zlib=*(0\|1)***\] \[**--complevel=*(1-9)***\] \[**--shuffle=*(0\|1)***\] \[**--fletcher32=*(0\|1)***\] \[**--unpackshort=*(0\|1)***\] \[**--quantize=*var1=n1,var2=n2,..***\] *netcdf3filename* *netcdf4filename*\

## DESCRIPTION

This manual page documents briefly the **nc3tonc4** command.

**nc3tonc4** is a program that converts a netCDF 3 file into netCDF 4 format, optionally unpacking variables packed as short integers (with scale\_factor and add\_offset) to floats, and adding zlib compression (with the HDF5 shuffle filter and fletcher32 checksum). Data may also be quantized (truncated) to a specified precision to improve compression.

## OPTIONS

These programs follow the usual GNU command line syntax, with long options starting with two dashes (\`-'). A summary of options is included below.

- **-h**

  Shows a summary of the available options.

- **-o**

  Overwrite destination file (default is to raise an error if output file already exists).

- **--vars**

  A comma separated list of variable names to copy (default is to copy all variables).

- **--classic=(0\|1)**

  Use NETCDF4\_CLASSIC format instead of NETCDF4 (default = 1).

- **--zlib=(0\|1)**

  Activate (or disable) zlib compression (the default is to activate).

- **--complevel=(1-9)**

  Set the zlib compression level (6 is default).

- **--shuffle=(0\|1)**

  Activate (or disable) the shuffle filter (it is active by default).

- **--fletcher32=(0\|1)**

  Activate (or disable) the fletcher32 checksum (it is not active by default).

- **--unpackshort=(0\|1)**

  Unpack short integer variables to float variables using scale\_factor and add\_offset netCDF variable attributes (it is active by default).

- **--quantize=(comma separated list of variable name=integer pairs)**

  Truncate the data in the specified variables to a given decimal precision. For example, 'speed=2, height=-2, temp=0' will cause the variable 'speed' to be truncated to a precision of 0.01, 'height' to a precision of 100 and 'temp' to 1. This can significantly improve compression. The default is not to quantize any of the variables.

- **--quiet=(0\|1)**

  If set to 1, don't print any diagnostic information.

- **--chunk=(integer)**

  The number of records along unlimited dimension to write at once. The default is 10. It is ignored if there is no unlimited dimension. If chunk=0, it means write all the data at once.

- **--istart=(integer)**

  The number of the record to start at along unlimited dimension. The default is 0. This option is ignored if there is no unlimited dimension.

- **--istop=(integer)**

  The number of the record to stop at along unlimited dimension. The default is 1. This option is ignored if there is no unlimited dimension.

## SEE ALSO

[**ncinfo**(1)](/ncinfo/1.md), [**nc4tonc3**(1)](/nc4tonc3/1.md).\

## AUTHOR

This manual page was written by Ross Gammon \<rossgammon@mail.dk\> based on the options displayed by nc3tonc4 -h.