I agree with the answer that a typical female boa sould be 8 feet (ish). I do disagree with the statement about as long as you don't powerfeed, it will stay small. I have a 11' female I didn't powerfeed, never been bred. Not even real thick, just loooong. I got her from EBV in 1989 as a baby. That makes her about 16.5 years old, which (from what I hear) would be unusual for a "power-fed" snake.
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Thanks,
Dave "Rainbows-R-Us"
0.1 Wife (WC)
0.2 kids (CBB)
4.12 Brazilian Rainbow Boa
1.0 Hypomelanistic BRB
0.1 Het for Hypomelanistic BRB
0.1 BCI "Elvira" normal from 1989
1.0 BCI albino / het-anery
0.1 BCI Hypo / het-albino
0.1 BCI Anery / het-albino
0.1 BCI Hypo (possible super)
1.0 BCI albino het stripe
1.0 BCI salmon hypo
0.1 BCI ghost
lots.lots.lots feeder mice and rats 