There was no magic sheet on capacity planning as you believed. It is an estimation.
Capacity planning will only work for approximately 60%. Each table in the database requires different type of storage clause. Last week I was testing a table's storage space by changing different value for INITRAN parameter. I was surprised by the outcome. The rest of storage clause parameters are not changed. Number of rows inserted is 10000. Data block size 8K.
Case 1.
INITRAN 1
Number of blocks used for 10000 rows - 155
Case 2
INITRAN 5
Number of blocks used for 10000 rows - 165
Case 3
INITRAN 10
Number of blocks used for 10000 rows - 175
In every case the same data was inserted in the table. But I got different results just by changing only one parameter.
Then you can imagine by changing PCTFREE, PCTUSED etc values, how the storage space is going to be.

Today, hardware price is cheap. I can buy 60 GB disk for the price of 6 GB Disk what I paid 3 years ago.
DO NOT WASTE MUCH TIME ON CAPACITY PLANNING.