Does anyone know where I can find out the weight of a car seat?

I have a bad back and I would like to compare the weight of the Britax Companion, Chicco, Combi, and the Graco infant seats. Thanks =)

Britax Companion - Weighs 9 1/2 lbs. (without base)

KeyFit Infant Car Seat by Chicco - Weighs 16 lbs. (off the base)

Combi Connection - Weighs 8 lbs. (without base)

Combi Centre DX - Weight off base: 9 3/4 lbs.

Graco SnugRide Infant Car Seat with EPS Foam - Weighs 7 lbs. (without base)

Graco Infant SafeSeat Step 1 - Weighs 9 3/4 lbs. without base