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Calculating length of rolled metal

Does anyone know of a mathematical formula for figuring the resulting length of rolling metal from one gauge to another?

For example: If I rolled a piece of 1"x6",18ga. silver to 20ga. is there a useful formula to calculate the resulting length beforehand.?

Thanks for any help with this.

I think that someone posted an online calculator that works. Do a search. I have kept these records for years and just use simple ratios…Rob

This is the formula my civil engineer husband worked out for me:
Solving for: x=FW x FL x T2 FW=finish width
SW x T1 FL=finish length
SW=start width
T2=Finish gauge (expressed as inches)
T1=start gauge (expressed as inches)
x=start length
There is supposed to be a horizontal line between the FW x FL x T2 and the SW x T1. i.e.
You divide the FW x FL x T2 by SW x T1 to get x

The above formula was reformatted by my computer?
The formula is:

x = FW x FL x T2 divided by SW x T1

This is a page from one of my bench books. I have kept them since the early 70s. You won’t be able to make much sense out of them, but they document how much of one sizes stock I was able to make rolling or drawing another specific length or weight sized stock. To use this data again, you set up a simple ratio. It has always worked for me +/- a bit. Keep lots of records of what you do, you might want to do it again…Rob

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There is an App iMakeJewelry with lots of calculators


No matter the formula you use, it will be an approximate calculation. Each rolling mill will be different. You will find it impossible to set the the rolling mill to be exactly the same each time. Your results may vary millimeters one way or another from an exact calculation. Remember that when you are trying to figure what you need. The calculation will get you close, but not exact. Do like I do when cutting cloth for a sewing project. But just a little more, and use it in the future for another project. I don’t mean to be negative, it is just the nature of what we do.

Once again, like Rob, I have notes that indicate how much a piece of wire was drawn out to. But some point I made the conscious decision that unless I had so little stock I had to worry or I was working with gold I wasn’t going to worry about how many inches of wire I could draw out of what. The same with rolling metal. So many grams of metal starting at a specific shape will give you only so many MM’s of material.

Very often if I needed more 20 ga. 1" disks I would weigh a disk, melt that much and more scrap and new metal. Roll out what I needed and punch a few disks.

I have often wondered(But never tested it) if 12" of 4mm x 4mm wire rolled to 2mm x 4mm would roll out to something near 24" of stock, minus a little loss. Can it be that simple?


Thanks to everyone for helpful responses.

thanks. i bought it.

Harold O’Connor’s bench book has a reasonable chart.