Formula for calcualting qty at given std size.

Hi Folks,
Can anybody tell me if there is a formula to help calculate materials required (ie 3000mm worksurfaces, WITHOUT JOINS). For example, if I need 4x cut pieces of work surface each at 1600mm and the stock length is 3000mm I clearly need 4 lenghts of worksurface.
This example isn't beyond even my meagre brains capacity but often the quantities are much greater and sizes of individual pieces varied.
Clearly adding the total lengths together and dividing by the stock size doesn't help as this results in joins.
Hope I've described the problem clearly, hope you guys can help where nobody has ever been able to.
Cheers,
Gene Stevo.

assume your stock lengths are 20, 22, 25 and 28

Today you want 50 lengths of 6

calculate wastage for each size, by eg 20-int(20/6)*6 =2

choose the lowest wastage factor EASY but think again, try the same exercise for 12, 18, 24 etc.

but you now want 10 lengths of 6 and 12 lengths of 7

again find lowest wastage factor for L=6 and L=7 after first checking if a length of 12 or 13 or 14 gives a lower waste factor

for 3 lengths 6,7,8 as before and check if 13, 14, 15 give less waste

You would need separate worksheets for all 1 size, 2 sizes, 3 sizes, 4 sizes etc - does this even start to help you?

Bob

Huge thanks to both Bob & Steve and sorry for late response to your messages.
I did try Steve's formula and it works a treat but unfortunately the circumstances don't fit. The calculation needs to take account of a wide variety of sizes, not just qty "x" by size "y".
For example a job may require 1x 2500; 2x 450; 1x 1890; 1x 1650 etc.

At the moment I just list the sizes into a column and drag the numbers into other columns, which have SUM functions ready formated to give a running total, and watch to see when I get near the number I first thought of. It works but it's a bit of a faff (esp when calcualting lengths of kick boards needed for a kitchen as there can be as many as 20 pieces all different lengths).

Thanks both for your help so far, greatly appreciated