Calculating stock size

[Tenebr0s]

I recently made a steel template for my knives, and am wondering how much extra volume I should calculate for my starting materials.  

 

For example, my template has a volume of 18 cm^3, and I am figuring a 20% loss of material due to scaling and grinding, so I figured I would start with roughly 22.5 cm^3 of steel.  Is a 20% loss way too optimistic?  What percentage of material do you guys normally plan on losing?

[Steve Sells]

what I lose wont really effect what you lose, try one and then you will know. too many factors. play it safe get a bar of steel aboutt the same size as you wish the finished blade. then see what is left over at the end, so you have a ref for the next time

[Rich Hale]

If you keep accurate notes on your work you can calculate that quite easy after you forge several dozen of the same size. with the same forge....

When I learned to make horseshoes from bar stock. I over worked the steel a lot. That caused it to thin and lengthen a lot and also narrow. The more I made the more consistent they became. After several large piles I could measure a horses foot. cut a bar of steel knowing how much it would stretch, and it would be correct size when forged. 

Same true for blades.  Make them and measure  make more etc...when they start measuring the wsame youir there...Keep in mind if you change blade shape, thicknews or size it will change everything. 

[Tenebr0s]

Thank you both for the replies.  I'll give these measurements a shot and see whether I end up right or not.