Originally posted by Mnemonical

For example:
if pctfree is 10%, pctused should be 75%
if pctfree is 5%, pctused should be 80%
if pctfree is 50%, pctused should be 35%
How far is this true?
F.
Very far!!!

Example :
DB_BLOCK_SIZE=4K
Table TTTT has avg_row_len=400 byte
Row_per_block ~9 max

Every day insert ~ 1000 new records.
Avg delete ~5% rows
Business procedure has 3 steps:
1) insert row (with initial information) ~ 100 bytes avg len
2) 1 week later each row should be upbate and add +50 bytes to avg len
3) 2 weeks later each row should be upbate and add last +250 bytes to avg len

How we should calculate PCT_FREE, PCT_USED
If we set :
if pctfree is 10%, pctused should be 75% ~= 90% rows will be chained (and near 100% of db_blocks)
if pctfree is 50%, pctused should be 35% ~= 25% rows will be chained

base on information about 1step ~ 35% alg len of record (then PCT_FREE ~ 30-35%)
base on information about 5% deleted rows:
PCT_USED ~ 35-( 9*0.05*400)/4000 ~= 25(or 30%)

Conclusion : use LMT