Grain Substitute for Dark Malt Extract

[osnoz]

Hi I'm a malt extract brewer, I'm trying to substitute dark malt extract (syrip) for pale malt extract (syrip) + assorted malt. I'm trying to replace Brewpacks dark malt extract, I'm guessing the malt required would include crystal , black and chocolate , but in what quantities?

All suggestions greatly appreciated.

 

[evanvine]

You will need to use 30 - 40% more grain by weight.
ME syrup gives c. 400 gravity points per kg per ltr
Malt gives 300, and Crystal gives 240