MD11 FLC HAS SMOKE IN COCKPIT. DECLARES EMER.

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SMOKE OF UNKNOWN ORIGIN WHILE IN CRUISE. EMER LNDG IN ATL; RWY 11; VFR. NO DAMAGE; NO INJURIES. SIT WELL HANDLED BY BOTH FLC AND CABIN CREW ACCORDING TO ESTABLISHED PROCS. WHEN ASKED BY THE FO WHAT TO ENTER ON THE FMS FUEL DUMP PAGE; I RESPONDED WITH THE DEFAULT WT OF 430K; POUNDS (NO CHANGE). HOWEVER; I ADDED THAT THIS WOULD GIVE US 80K POUNDS OF FUEL REMAINING. WE WERE BOTH ON OXYGEN AND MY MIKE PICK-UP WAS WEAK UNLESS I HELD IT CLOSE TO MY LIPS. ALL THE FO HEARD WAS THE END OF MY STATEMENT; SO HE SET 48000 POUNDS IN THE DUMP WINDOW. I MISSED IT! WE LANDED 45000 POUNDS OVERWT; BUT WELL WITHIN RWY ALLOWABLE; THANKS TO RELIEF PLT; WHO CAUGHT ERROR. LESSON: ANSWER THE QUESTION AND KEEP IT SIMPLE WHEN IN THIS TYPE OF SIT. SUPPLEMENTAL INFO FROM ACN 556647: AS IN A LOT OF SCENARIOS SUCH AS THIS; COM WAS A KEY FACTOR IN THE OUTCOME. CONTINUED PRACTICE DURING SIMULATOR TRAINING WORKING VARIOUS ABNORMAL SITS WITH THE OXYGEN MASKS ON WOULD BE HELPFUL. A MISCOM OCCURRED DURING OUR SCENARIO ABOUT HOW MUCH FUEL WE WOULD DUMP AND HOW MUCH WE WOULD WEIGH UPON LNDG WHICH RESULTED IN AN OVERWT LNDG BY 45K LBS. ALL PARTS OF THE INCIDENT WERE EXECUTED WITH GOOD CRM AND THE CAPT FACILITATED THE SAFE OUTCOME WITH HIS LEADERSHIP AND SKILLS.