# Calculating the number of index blocks required

Use the formula that is shown in Figure 1 to calculate the number of index blocks required. Use the result as the value of B in Formula for the RACF database size.

Note:

- The values of
`F`

through`Z`

and`AA`

through`VV`

are described in Calculating the number of blocks required for the profiles. - The formula for
`B`

is equivalent to:`B= D/E`

^{1}+ D/E^{2}+ … + D/E^{9}+ D/E^{10} - The formula for
`E`

assumes that the index blocks are half full (.5). If you can extend an existing RACF® data set with the IRRUT400 utility, then you can determine (with the IRRUT200 utility program) how full the index blocks are on the existing data set and replace the .5 value with a value that you determine. In this case, you can also consider the compressed name length when you specify the average index name length.