The 2005 Hildebrandt Law Department Survey reports the figure of $192 per hour per lawyer, fully loaded. You can do several things with your own number. You can look at the blended hourly rates of your outside counsel and match them to the fully-loaded cost of your inside lawyers, (See my post of Sept. 5, 2005 on European law departments at about $220 an hour, Sept. 25, 2005 about using 1,850 chargeable hours as a proxy, and Oct. 18, 2005 on how to calculate your figure.)
You can track the cost over the years and see how it changes with revenue or the Consumer Price Index. You can even figure the cost for your various business lawyer groups or specialty groups, after making some assumptions about shared overhead.