Saturday, June 28, 2014
DIY Calculations for Hexagon Quilts aka Epic Quilt Math
Funny things, those hexagon quilts. Since the patch is an odd shape, it is a challenge to figure out exactly (or even vaguely) how many hexagons of a given size would be needed to make a specific size of quilt. After a recent email asking just that question, I have decided to bite the bullet and figure it out for us all!
My calculations and recommendations for yardage and "metre-age" are skewed toward the generous, so you might need fewer hexagons or a bit less fabric than what you see here. Better to be safe than sorry. Please take the fabric requirements at the end as estimates, not gospel.
To make things easier, we will deal with the idea of a 10" finished section of hexagons. We will call this our "block." Let's start with how many hexagons (in different sizes!) it takes to cover a 10" block. (The hexagon measurements refer to the finished measurement of a single side of the hex.)
Number of hexagons per 10" block:
1/2" hex = 208 hexagons (whoa!!)
3/4" hex = 92 hexagons
1" hex = 52 hexagons
1 1/2" hex = 23 hexagons
Ok! Now let's have a look at how many hexagons are used in a few common arrangements of Grandmother's Flower Garden (GFG). These quilts are typically composed of Flower Units (either a single round of petals around a centre or a double round of petals around a centre). These Flower Units are either set directly next to each other, or set with a single "path" of a background fabric between them, or a double "path" of background fabric.
Let's start to break down those numbers now:
Single round flower (Centre + single round of petals) = 7 hex total (centre + 6 petals)
Double round flower (Centre + double round of petals) = 19 hex total (centre + 6 petals + 12 petals)
Now, with background "paths" between flowers:
Single round flower + single "path" of background fabric = 14 hex total (7 for the flower + 7 background)
Double round flower + single "path" of background fabric = 29 hex total (19 for the flower + 10 background)
Single round flower + double "path" = 19 hex total (7 for the flower + 12 background)
Double round flower + double "path" = 37 hex total (19 for the flower + 18 background)
Let's plan a quilt!
Say, you want to make a queen sized hexagon quilt. My Master Size Guide says that a queen quilt with a 12" drop (the quilt hangs over the bed on the sides and at the foot) is 84" x 92." For our planning purposes, let's round those numbers up to the nearest 10. We will plan for 90" x 100" for buying our fabric.
A 90" x 100" quilt means 9 blocks x 10 blocks (remember, we are working with a 10" block). That makes a total of 90 blocks.
Multiply the number of blocks you're making by the number of hexagons per block in the size of hex you want to for with. For example, you want to make your quilt using 1" hexagons. One block would require about 52 hexagons. So, 52 hexes x 90 blocks = 4,680 hexagons. (If you're using tiny, 1/2" hexagons, you would need 18,720 hexagons! Yikes!)
Let's work with that 1" hexagon for now. Depending on your design, you just need to divide the total number of hexagons (4,680) by the number of hexes in your Flower Unit, whichever one you decide to work with. Let's do Double round flowers with a single path between flowers. That type of unit requires 29 hexagons in total.
4,680 divided by 29 = 161.4 Flower Units. We'll say 162 units. To break it down further, each unit needs a centre (162 hexes in all), a first round of petals (6 x 162 = 972 hexes in all), a second round of petals (12 x 162 = 1,944) and background "path" fabric (10 x 162 = 1,620 background hexes in all).
Whew! Ok! Now we need to know how many hexagons of a given size can be cut from our fabric. The estimates I'm using here are slightly generous. You will likely get a few more hexagons out of your fabric than what I'm telling you here, but again, better safe…
1/2" hexagons = 168 per Fat Quarter (FQ), 672 per yard or metre
3/4" hexagons = 99 per FQ, 396 per yard or metre
1" hexagons = 56 per FQ, 224 per yard or metre
1 1/2" hexagons = 30 per FQ, 120 per yard or metre
Most of time, folks are working "scrappy" for the Flowers, but these numbers will give you a rough idea of the total amount of fabric you will need to have on hand. The only fabric you might likely buy in quantity is the fabric for the centres (the same centre throughout the quilt can serve as a unifying element), and the background fabric.
Our theoretical quilt needs 1,620 background hexagons.
1,620 divided by 224 (the number of 1" hexagons we can get out of a yard or metre) = 7.25 yds or m.
That is a lot of fabric. Better safe than sorry. On a side note, since the background requires so much fabric (lots of small shapes require a heck of a lot of seam allowance to get them together), I would guess that this is the reason that background "path" fabric in vintage GFG quilts is often white or natural muslin. These choices could be, and can still be, purchased in the large quantity required for a more reasonable cost than fancier prints or even coloured solids.
Let me know if this has been helpful! (Or, if you needed to take an Advil after reading it.) I'm going to go have a nap...