Limit Electronic Devices on Airlines to 300 mm and 200 g?

The US and UK have banned electronic devices larger than a cellphone from aircraft cabins on flights from some countries. But what is “larger than a cellphone”?

Perhaps airline check-in counters need a gauge, like the one for carry-on luggage, or weight alone would be sufficient.

It is not clear what the threat from laptops and tablets is. There could be good reasons for authorities are not wanting to make this clear, but I don't know what they are.

The Guardian article mentions the risk of bombs and of lithium batteries. The bigger and heavier the device is, the bigger the bomb or battery it can hold. So it would make sense to limit the size of devices, but to do that an actual size needs to be specified, not just “larger than a cellphone”.

Large phones ("phablets"):

• iPhone 7 Plus, with a 5.5 in screen is 158.2 mm x 77.9 mm x 7.3 mm and weighs 188 g.
• Samsung Galaxy S7 Edge with a 5.5 in screen is 150.9 mm x 72.6 mm x 7.7 mm and weighs 177 g.

Are not that much smaller than a small tablet:

• Samsung Galaxy Tab 7.0 with a 7.0 in display is 190.09 mm x 120.45 mm x 11.98 mm and weighs 380 g.

A reasonable limit for devices might be: height, width and depth added (the way baggage sizes are set), must be no more than 300 mm and the weight no more than 200 g. That would allow the phablets, but not tablets.

Just to check, my chunky old Lenovo A588T Android Flip Phone is 120.6 mm + 62.5mm + 16.8mm = 199.9 mm at 178.4 g,. That would pass, provided I don't open the flip, which makes the phone 115 mm longer. ;-)