Commenter Kiwi Geoff kindly wrote a program that calculates LDL using the Friedewald equation and the equation from this paper, which may be more accurate for people with a total cholesterol over 250 and triglycerides under 100. For people whose triglycerides are over 100, the Friedewald equation should be relatively accurate. You can plug your total cholesterol, HDL and triglycerides into the program (in mg/dL), and it gives you both LDL values side-by side. Here it is:
LDL Cholesterol Calculator
Thanks, Geoff.