axle weight calculator?

Hello,

I'm looking at putting together a straight truck with a water tank and a few other things on the back. I want to put the 20k+ lb(full) tank as far forward as possible without being overweight on the front axle.

On this forum a while back i found an axle weight calculator for this type of calcuation using excell that someone had put together but cant locate it again. Anyone help?

I'm trying to figure out if a 12k lb front axle will work or if i need to look for a heavier one.

thanks