Sunday, August 29, 2010

How to plan a cot sized quilt using metric maths...

Even though the battings I buy are 50" by 60" I still do all my actual math in metric. In metric, these battings come out to about 152 by 127cm. Ish.

I'm a big lover of fat quarters. I have tubs full of them, since they're not only practical, but often cheaper than buying off the bolt, if you do your homework, and look around.

As a result, most of my designs are fat quarter based. BUT, not all fat quarters are created equal.

Put simply, METRIC fat quarters are better, by about 10%. By better, I mean bigger. A fat quarter from the big box at Stitch and Knit (my local specialist quilt shop, where precut in store fat quarters are $3 each, which is great since off the bolt is usually $20 a metre) is about 55x50cm, whereas a fat quarter from America (be it from eBay or as an imported precut bundle at Stitch and Knit) is usually 55x45cm. A cot sized quilt uses at least 12 fat quarters. Add up the difference and that's over one full fat quarter of fabric less.

Earlier quilts were a bit more wasteful with regards to the design, the cutting and the layout. The retro quilt uses the equivalent of 16 fat quarters, with half of 4 of them not actually included in the quilt. The blue green quilt uses 14, and left a good batch of scraps in its wake. By the time I got to Ester's quilt I had my math down pat.

Instead of a quarter inch seam allowance, I use 7.5mm, which is closer to 3/8ths of an inch. This means a bit more wastage with regards to visible use of fabric, but a bit more security, and much easier (metric) math. This is because 7.5mm doubled is one and a half centimetres, whereas 6.4mm (a quarter inch) is a much more difficult to calculate and measure 1.28cm. Try using that in all your calculations, or cutting that accurately, and your brain will promptly explode.

So if the allowance is 7.5mm, and each actual seam (which is made up of two bits of fabric) is 1.5cm, then a block with one seam each way (which is most of my designs) will need to be 3cm bigger in each direction than it's finished size (1.5cm for the inside seam and 1.5cm to join the block to its neighbours)

An 8 block by 6 block quilt with a final size of 152 by 127cm therefore needs 48 rectangles of 22x24cm.

You can almost exactly cut 4 of these from an American fat quarter. And if each block has one join in each direction then from 12 fat quarters you'll have 48 blocks measuring 20.5cm by 22.5cm. And when they lose 1.5cm each in their coming together, their 19x21cm size will make a quilt top 152x126cm, assuming you've set them long side 6 across and short side 8 across.

If you have, you'll need to trim the batting by 1cm on one side. If you've done it the other way...

...Have you maybe considered some other kind of craft?

Now I just need to do some similar math for a baby blankie of 85 by 105cm. That's what I'll be doing tonight. Metric Math. The best kind there is.

No comments:

Post a Comment