Passengers at Heathrow Airport will no longer be able to take over-sized hand luggage on board flights.
Passengers can check their luggage in gauges installed in all terminals
From 1 August, any baggage which does not fit into gauges placed in all the terminals must be checked.
A spokeswoman for operator BAA said the move was designed to avoid queues caused by lengthy security checks on bags containing electronic devices.
Bags will have to be no more than 56cm long, 45cm wide and 25cm deep to be allowed on as hand luggage.
The BAA spokeswoman said: "Passengers are now packing larger, thicker hand baggage filled with more electronic devices than ever before.
"This trend demands extra security attention leading to longer queues.
"It's time for the over-stuffed wheelie bag to end at check-in."