We are trying to figure out the exact width what is the actual footprint size of this pool including the braces?

The 18ft length pool, on the side of the box, says 19ft10in x 10ft10in. That's the footprint out to the exterior supporting legs, per the diagram.

Per the picture, it looks like it just sits on the water. Does it have 'ties' or something to keep it from sinking?

No ties. It's a sturdy material designed to lay on top of the water. It works beautifully. So happy I bought it.

Does it matter if it does not cover the entire width and length of the pool? would we get a lesser warming effect ? Our pool is 30 ft by 18 ft

The cover is pretty good at warming to top foot of the water with the solar sun of the cover. It will likely not warm all the water at anytime. However it is a good cover, very durable and does keep the top pool from debri. I also have the roller bar, which makes it easy to roll on and off the pool. This was a great and easy way to use the cover before and after use.

Size	17' 8" X 8' 4"
Colour	Blue
Material	Polyethylene (PE), Vinyl
Brand	Intex
Product Dimensions	5.49L x 2.74W Meters
Style	Solar cover
Item Weight	3.08 kg
Special Feature	Durable
Shape	Rectangular
Closure Type	Pull on
Pattern	Solid
Installation Type	Floating
Global Trade Identification Number	10078257316622
UPC	078257316625 647095466542 799331647342
Item model number	29026E
ASIN	B006MDQZHG

Intex Solar Cover for 18ft X 9ft Rectangular Frame Pools, Measures 17' 8" X 8' 4"

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