I have seen attempts at it. One is to multiply your estimates by the number of different pieces you're estimating. So, if you have estimated for three differe

I have seen attempts at it. One is to multiply your estimates by the number of different pieces you're estimating. So, if you have estimated for three different pieces, multiply those estimates by 3 when deciding how much the whole thing will take. If you have estimated for five different pieces, multiply the sum by 5, etc. The idea is that the more estimates you have made, the more likely that at least one of them will "blow up" and take far longer than expected. Generally speaking, though, software is far less advanced than civil or aeronautical engineering in this kind of thing.