How to use the hexagon quilt calculator
- Enter the finished side length of one hexagon in inches.
- Choose a rosette, a flower of rings, or a honeycomb that fills a quilt of a given width and height.
- Set the rings, or the quilt size, and open the advanced options to change the seam allowance, fabric width and cutting efficiency.
- Read the number of hexagons, the layout size, the cut sizes and the fabric needed.
Formula
Hexagon with side s: width flat to flat = sqrt(3) s, point to point = 2 s, area = (3 sqrt(3) / 2) s^2
Cut side with seam allowance a: s + 2 a / sqrt(3)
Rosette of r rings: 1 + 3 r (r + 1) hexagons; across the flat sides (2 r + 1) sqrt(3) s; point to point (3 r + 2) s
Honeycomb columns: floor((W - 2 s) / (1.5 s)) + 1, alternate columns half a hexagon lower
Fabric = patches x cut area / (fabric width x efficiency)
A regular hexagon is made of six equilateral triangles with side s. A seam allowance of a on every edge moves each edge outward by a, which lengthens each side by 2a / sqrt(3).
A three-ring rosette and a throw quilt
With a 1.5 inch side, a hexagon is 2.598 inches flat to flat, 3.000 inches point to point and 5.846 square inches. With a 0.25 inch seam allowance the cut side is 1.789 inches and the cut area 8.312 square inches. A rosette of 3 rings has 1 + 3 x 3 x 4 = 37 hexagons, 18.19 inches across the flat sides and 16.50 inches from point to point.
The 37 patches need 307.6 square inches of fabric, or 9.8 inches of 42 inch fabric at 75% efficiency, about 3/8 yard. A honeycomb of 2 inch hexagons for a 50 by 60 inch throw has 16 columns and 264 hexagons, filling 49.00 by 58.89 inches, and needs 3 1/4 yards.
Rosettes and honeycombs
A rosette starts with one hexagon and adds rings: the first ring has 6 hexagons, the second 12 and the third 18, so the total grows as 1, 7, 19, 37, 61. Rosettes are the classic "grandmother's flower garden" block and are often joined by a ring of a different color. The honeycomb layout covers a whole quilt with hexagons in columns that interlock, so the edges are zigzag unless you add half hexagons to square them off.
The counts here are for whole hexagons only. Half hexagons for straight edges, borders and sashing are not included.
Cutting and fabric
Whether you piece by hand over paper or by machine, the cut patch is larger than the finished hexagon by the seam allowance. The page converts a seam allowance to the cut side, and then estimates fabric from the area of all the patches divided by how much of the fabric you expect to use. The efficiency of 75% is an example: arranging hexagons carefully on the fabric or cutting strips first can do better, and directional prints do worse.
Related tools: the quilt block size calculator, the quilt backing and binding calculator, the quilt sashing and border calculator, the precut quilt calculator, and the hexagon grid paper generator for printing templates.
Assumptions and limits
- Hexagons are regular, with all sides and angles equal, and fit together with no gaps.
- The seam allowance, fabric width and cutting efficiency are example values you can change.
- The honeycomb count covers whole hexagons only and leaves a zigzag edge.
- Backing, binding, borders and spare patches are not included in the fabric.
Frequently asked questions
How is the side length of the hexagon defined?
It is the length of one edge of the finished hexagon, measured without the seam allowance. For paper piecing it is the edge of the paper template. The cut patch is slightly larger.
Why does the cut size change with the seam allowance?
Adding a seam allowance on each edge pushes every edge outward, which makes the whole hexagon bigger. The apothem grows by the allowance, and the side grows by 2 times the allowance divided by the square root of 3.
How many hexagons are in a flower with a given number of rings?
One in the center, plus 6 in the first ring, 12 in the second, 18 in the third and so on. The totals are 1, 7, 19, 37, 61, which is 1 + 3 r (r + 1) for r rings.
Can I use this for hexagon sizes given across the flats?
Yes. Divide the width across flat sides by 1.732 to get the side length, then enter that. For a 2.598 inch hexagon across the flats the side is 1.5 inches.