Quiltingboard Forums - I'm making a pattern larger - how do I figure how much extra fabric??

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This is driving me crazy.... my brain just doesn't work on things like this. The pattern I'm looking at is in the Layer Cakes, Jelly Roll, and Charm Quilts book (if you have the book, it's called Blossom Time (there's another pattern out there with the same name, but very different). Anyway, it's got a 6" border, with flowers made from 4 5" charm squares - there are 4 across and 5 down (20). The sashing around each flower is cut at 2-1/2", so I guess the final stitched width is 2". Finished quilt size - 58" x 69". The directions say to use 1-3/4 yd for the sashing and inner border (which is basically the sashing) and 1-3/4 yd for the outer border and binding. When someone else posts #'s like this I glaze over, so I'm hoping one of you can understand this! :lol:
Anyway, I wanted to add another row of flowers on the side and bottom - so adding 11" (finished) to each side (right?) making it 69" x 80".
My dilemma - how much extra fabric do I need for the sashing/inner border and how much extra for the outside border/binding?
Also, they didn't say how much for backing - a little over 4 yds? 4-1/2?
I love the dreaming and sewing part of quilt making, but the math really shuts me down! :shock:

Wow, this is moving fast!

I hate the math part, too. Generally, I whine until my husband does the math for me. Once when he was away on business for two weeks, I downloaded this free trial and used it to calculate how much of two different fabrics I needed for a block.
It worked out OK for me.

http://www.quiltmath.com/download_quilt_math.html

Just using rough measurements, you are increasing the quilt by 20%.

(69/58=1.189) or 1.2
(80/69=1.159) or 1.2

I would multiply the fabric requirements by the increase ratio so 1.75x1.2=2.1

Since I always buy more, I'd go for 2.5 yards.

Ok, that's good, that helps... I'd rather have more than not enough, just not tooooo much. Thank you!

You're good Madquilter!! :<)

Would you say 4yds is good for the backing? Or should I go more?

I think four yards is plenty.

As usual, thank all of you for your help! :D