Could somebody help me with the math?
 

This is a picture of the pattern I used to make a table runner. I would like to adopt the pattern for a queen size bed quilt. I have a fat quarter bundle with 37 co-ordinating prints. If I start out using 5-1/2" squares, which I think would use most of a fat quarter with the littlest waste (correct me if there's a better size to start with), how big of a quilt top will I be able to achieve? Thanks!

ok. very rough estimate.
37 fat 1/4 cut to 5-1/2 sq = 9 sq per fat 1/4 = 333 sq
this would make about 66 1/4 sq triangles and 66 5" sq giving about 132 squares at 5"
finished size would be 4-1/2
11 across = 49.5" and 12 down = 54"

these are, as i said, rough. i will not be too embarrassed if someone proves me to be completely wrong.
good luck.

It looks like half your blocks are QST's, so if they are cut from 5.5" squares then the resulting blocks will be only 4.25".

Personally, I would be more concerned about making perfectly sized QST blocks.

Dunster's math, as always, is correct - for QST blocks the starting squares are always at least 1.25" larger than the desired FINISHED size of the block.

And that works if the cutting, sewing and pressing are all PERFECT.

I always cut my starting squares bigger so I can trim the blocks, once assembled, down to the UNFINISHED perfect size.

If you find the 5.5" size is the most efficient size to cut from the fat quarter, I'd count on 4" FINISHED blocks (so the blocks would be trimmed down to 4.5" UNFINISHED).

Keep in mind, though, that scale is very important. What looks great and appropriate on a 27 block small runner placed on a 48" table will look totally different on a queen size bed.
Not necessarily wrong, but it's just something you should be aware of before you start cutting.

Here are two examples.

Assume your FQ collection is made up of perfectly cut 18"x22" FQ's (and that's a big assumption).

You'll get twelve 5.5" squares from each FQ.
But in reality, only six squares will be used in the making of the QST blocks, as the other squares will be plain - cut 4.5" UNFINSHED.

Let's make life simple, though, and assume from the 37" FQ's, you'll get the equivalent of 444 squares (37x12) - half will be QST blocks and the other half will be plain alternating blocks.

Using a 20x22 block layout of 4" FINISHED blocks will create a quilt top 80"x88".

The second pictures illustrates using blocks that are 7" FINISHED - starting blocks were cut 8.5" (with some wiggle room).

Each FQ would render four starting squares (again, half will end up in the QST blocks and half will be plain), for a total of 148 blocks from the 37 fat quarters.
And, yes, you'd have some left over strips - but they could always be incorporated into the border, or used on the back.
Using a 12x12 block layout of 7" FINISHED blocks, the quilt top would be 84"x84".

Both of these are the the same pattern, (almost) same sized quilt tops - different sized blocks.
You can test it by making some scrappy 4" blocks and tossing them on your bed to see how you like the size.

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Gosh, I'm sure glad I put the question out there. I definately don't like the looks of the top picture! Kinda too tired to read all this good information tonight, I'll look at it tomorrow. Just wanted to thank all for your comments!

that was very helpful to see the difference

Dunster, would it help her any if she used an Easy Angle to cut her triangles? I'm making a Jewel Box quilt for our daughter. Using fat quarters of batiks for a quilt that will be 108x108. Only using 24 fat quarters, I have all the HST's made, working on the 4 patch units, and have some of each fat quarter left over. I used the Easy Angle for all this.

Oops, I forgot to say that the blocks in the quilt finish at 4". The directions called for cutting 5" squares, placing light and dark right sides together, sewing diagonally from corner to corner. I did get 24 - 4 1/2" triangles and 24 - 2 1/2" squares from each fat quarter with fabric left over from each.

@sadyms - Just an FYI but it is impossible to make a quilt top measuring 108"x108" from only 24 FQ's (6 yards of fabric without even starting to account for any seam allowances). Perhaps they were half yard cuts?

QST blocks require more fabric than HST blocks - there's that extra seam.

For each HST triangle block the starting squares need to be 7/8" larger than the desired FINISHED block.
Again, that's perfect cutting, sewing, and pressing.

For either block, though, each starting square will render a finished block - in the mzzz's case, a QST or plain block.
And her design doesn't require the smaller squares. She will still have fabric left over.

Both quilts are getting 12 starting squares from each FQ, with some left over.

@mzzzquilt - Here's a diagram of how the FQ would be cut for the pattern you're making - the six larger squares are the 5.5" starting squares for the QST blocks (includes a bit of wiggle room), and the six smaller squares are the 4.5" UNFINISHED plain alternate squares. The black represents the remaining fabric.