The Windows 2000 Resource Kit contains Dureg.exe - Registry Size Estimator.

"DuReg is a command-line tool that enables you to discover how much data is stored in the registry, or in any registry subtree, key or subkey. Additionally, the tool also enables you to search for all occurrences of a text string in the registry. This search can be limited to a specific subtree.

DuReg counts data, not space. Because the space any data occupies varies with the storage method and amount of free space available, the size of data and size of space consumed are not equal. Also, because it measures data, DuReg does not account for fragmented free space in the registry.

The DuReg helps developers and administrators estimate how much space registry data is consuming.....

The registry data size function is unique to each system. You can determine the maximum registry size and an estimate of the current registry size by using System in Control Panel. You can also find the current:maximum size ratio (expressed as a percentage) by using the System: % Registry Quota in Use counter in Perfmon\Sysmon. However, only DuReg returns the size of individual keys and subkeys."

Syntax:

dureg \[\{/cr | /cu | /u | /lm | /a\}\] \[\{/s | /d\}\] \["registry_path"\] \["string to search"\]

Where:

<b>/a </b>                  finds the size of entire registry (all).
                            <b>dureg /a</b> returns:
                            Size of HKEY_CLASSES_ROOT   :    6181756
                            Size of HKEY_USERS          :    1565865
                            Size of HKEY_LOCAL_MACHINE  :   12367471

                            Total Registry data size:    20115092

/cr "registry_path" Sizes <b>HKEY_CLASSES_ROOT</b>. Include a registry path
                            to find the size of any key within this subtree.

<b>/cu "registry_path"</b>  Sizes <b>HKEY_CURRENT_USER</b>. Include a registry path
                             to find the size of any key within this subtree.

<b>/lm "registry_path"</b>  Sizes <b>HKEY_LOCAL_MACHINE</b>. Include a registry path
                            to find the size of any key within this subtree.
                            For example, <b>dureg /lm "software\microsoft"</b>
                            finds the size of the <b>HKLM\Software\Microsoft</b> key.

<b>/u "registry_path"</b>   Sizes <b>HKEY_USERS</b>. Include a registry path
                            to find the size of any key within this subtree.

<b>/s</b> "string"          searches for the "string" in the registry.
                            For example, <b>dureg /s "video"</b>
                            finds all occurrences of "video" in the registry.
                            <b>dureg /lm /s "video"</b>
                            finds all occurrences of "video" in HKLM.  
                            <b>dureg /s /lm "Content Type"</b> returns:<b>
                            HKEY_CLASSES_ROOT\MIME\Database\Content Type\application/fractals\Extension : .fif
                            HKEY_CLASSES_ROOT\MIME\Database\Content Type\application/hta\CLSID : \{3050f4d8-98B5-11CF-BB82-00AA00BDCE0B\}
                            HKEY_CLASSES_ROOT\MIME\Database\Content Type\application/hta\Extension : .hta
                            HKEY_CLASSES_ROOT\MIME\Database\Content Type\application/mac-binhex40\Extension : .hqx
                                             .
                                             .
                                             .
                            HKEY_CLASSES_ROOT\MIME\Database\Content Type\video/x-msvideo\Extension : .avi</b>                              

             
<b>Note:</b> To stop a search, press <b>CTRL+BREAK</b>.