It is not difficult to estimate the correct amount of material needed for a project.

If you know that a standard role of vinyl or fabric is 54 inches wide,by a running yard of 36 inches then simply measure that individual panels in the seat (length and width) to get a rough spare dimension.
Record these boxes onto a sheet of paper and chart out a cutting plan. Also allow for welt and add an extra quarter of a yard.

You will never be short or have more that you need if you just take the time to measure each project.

I do it the same way. With leather its a little bit more difficult. Here its depend on the quality of the hide. I had learned you need calculate 30% cut off. I have cutting templates for a lot of cars. So i can lay out all samples and can find out the best way to cut out my parts.
Also if I use expensive leather, I first make a pre-cut of cheap material to find out the best way for the leather. On this way I think I save nearly one hide my last Connolly Project. But the cut off on old Bentley is horrible :s

Yeah we do the same, make cutting plans and keep wastage down to a minimum. We also have a range of cutting plans prepared for repeat jobs.But then it's easier for us as all our work is from fabric/vinyl off the roll and no leather.

I generally do the estimating in my head. picturing the parts laid out like Fred's picture above. But there are some days my brain just wont cooperate and I end up doing the paper sketch with measurements

Estimating leather is very similar. An average hide is 48 to 52 square feet. A square yard of vinyl is 18 feet. Due to flaws in the hide it will vary our yield, but a hide is almost 3 yards of 54 inch wide vinyl.

@Jens Jesberg pre-layout of the actual pieces is always a safe bet when working with leather.

We are currently making a Porsche 356 and the customer has opted for the Porsche natural leather from Hans Reinke. Despite templates, the cut off is extreme. I will probably take it out of the customer selection. If one of you uses the Reinke leather I really advise you of the nature leathers. The quality really not very good. And not everything can justify as natural marks.:s

Jens, when you say cut off is that material that is unusable?
I've had leather supplied for porsche from a uk supplier and found it not very nice, its been hard and coated with something that makes it impossible to mark,ie with pen, pencil, chalk.I also used a hide from another supplier which was similar, not a cheap hide either.

what leather supplier are you using keith ??

private message sent Chris.

Pleats and channels use at least 25% more material, don't forget to allow for them.