St Pancras International station is a separate building to Kings Cross - so I never know how long to leave between my tube arriving into KX and my train departing St Pancras. Today I had some spare time, so I decided to use my stopwatch !
Starting point - Piccadilly line eastbound - Carriage two, door three - by the exit
Speed - normal pace, not rushing it - although it was early morning, so not many backmarkers to navigate around
Escalators - sauntered up them
Luggage - smallish backpack
Routing - exited to outside up the steps as soon as passed through the tube barriers. Probably slightly quicker than using the tunnel underneath Pancras Road (but that routing has the advantage of escalators to take you upstairs into St Pancras station)
Exiting Piccadilly line to Platform B northbound - 5 mins 15 seconds
It would be slightly less to Platform A southbound
Exiting Piccadilly line to Platforms 1, 2 & 3 upstairs - 6 mins 35 seconds
It would be an extra 30 seconds or so if your train was the far end of the platform (as often happens)
Exiting Piccadilly line to Eurostar security - 5 mins 45 seconds
Next time I won't bother giving myself a full 15 minutes to spare !