Backing size.
 

I made a large quilt that I want to put on our queen size bed as a spread and that will also cover both the mattress and box spring. I am going to add a 12"panel to the backing so I need to know how much fabric I would need. I am open to the wide (106") fabric and I would add the 12" piece down the middle or use regular size width fabric, also using the 12" panel. I don't know how much fabric I would need. I have an idea by using my figures but would like what some of your ideas would be. Right now the top measures 110 inches wide and 98 inches top to bottom. The extra 12" panel would go top to bottom and it is the same piecing and pattern as the quilt top. I know that is large but it has to be that for the size I want. I am 78 and my mind just doesn't work as good as it used to. Will appreciate any help. And guess what - I am going to FMQ it so that should be interesting. I have machine quilted large queens so what's a few more inches!!!?

For starters, I suggest putting that strip off-center.
because way off- center looks like it was done on purpose. Slightly off center looks like an oops.

I agree. I pieced a back that was too narrow that way and it came out great.

If you are putting the panel, vertically, you'll just need the length (98"?) plus however much you need around the edge. If you need to leave 10" on the edges that would be 118" or a bit over 3 1/4 yards (by my calculation 3.2777)

That is going to be a large quilt to handle all the way around the bed. Another option is to make a panel skirt for the box spring. They are easy to construct to the size needed. There are 3 separate panels to cover each side of the bed and the foot of the bed. Add a box pleat at each end of the panels.

A 4-6 inch piece of muslin added to the panel piece of fabric. These panels are simply tucked in between the mattress and box spring.

The way I see the easiest measurements.
Okay...I looked at this again & realized I had the panel as a crossways piece. I have to recalculate everything! So I am deleting the wrong info & will try again. Barb

Once again..... I was over thinking everything. Your flimsy size is 98 length by 110 width. You stated that the panel is going the length of the quilt which means it will be subtracted from the width.

A 106 inch wide x 3 yards will be wide enough for the 110 inch width of the quilt by the time you take out for the 12 inch panel you are inserting. And the 3 yard (108") length will cover the 98 inch length with 5 inches left for both the top & bottom.

Thanks all who responded. I think I can manage now and I do know about not putting the strip down the center but the reminder was good.