Determining Working Capital Needs -- Prior to Making Offer

The great debate is always whether working capital should be included or excluded.

For Buyers who EXCLUDE working capital from your transaction (thus avoiding the hassle of negotiating a w/c peg) -- how do you determine how much working capital is necessary (via Cash or a LOC) when penciling out your deal PRIOR to making your offer?

Just trying to determine how much will be necessary, so I can adjust my transaction multiple accordingly.