It depends on the color for one and also depends on what you're going over. Are you planning on using Basecoat/clearcoat or are you using single stage. Is it all one color or is it two tone like many of the FJ60's. More information would probably be required to give you a fair guesstimate on how much material you'd need. You didn't say if you were planning on doing the roof as well??
Is the vehicle currently in primer, will you be priming it first or is your intention to go directly over the OEM finish that has been sanded (probably the worst choice). All of these things play a role in how much actual color you'll need, so provide a few more details and I'll be happy to share what I've discovered.
Good luck!