Quilt math · Calculator
Dresden plate math: blades and angles
The angle for any number of blades, the strip to cut, and where the wedge ruler’s lines go, for a Dresden Plate of any size.
The short answer
Each blade’s angle is 360° ÷ the blades: 20 blades are 18°. For a 15″ plate with 6″ blades, cut 6½″ strips, lay the 18° ruler’s 2⅞″ line on the top edge and its 9⅜″ line on the bottom, and turn it each cut: 21 blades from a 42″ strip.
Work out yours
Free · no account20 blades of 18° · open center 3″ across
Wide end about 2⅜″, finished
The blade’s length + ½″. 1 strip of 42″ for all 20.
Its 2⅞″ line on the strip’s top edge, its 9⅜″ line on the bottom.
Turn the ruler each cut, top to bottom, so nothing’s wasted between them.
Quarter Inch has a Dresden Plate in its block library, and prints Template W at true size if you have no wedge ruler.
Open Quarter InchSame sums as the app: @quarterinch/cutting bladeCut · lines measured from the ruler’s point, ¼″ seams all around · the wide end to the nearest ⅛″
Blades and the angle
A Dresden Plate is a ring of wedge-shaped blades. The blades share the circle’s 360°, so each one’s angle is 360° ÷ the number of blades. The classic plate has 20 blades of 18°, cut with an 18° wedge ruler.
| Blades | Angle | Strip | Ruler’s lines | From a 42″ strip | Wide end, about |
|---|---|---|---|---|---|
| 12 blades | 30° | 6½″ | 2¼″ to 8¾″ | 13 | 4″ |
| 16 blades | 22½° | 6½″ | 2½″ to 9″ | 17 | 3″ |
| 18 blades | 20° | 6½″ | 2¾″ to 9¼″ | 19 | 2⅝″ |
| 20 blades | 18° | 6½″ | 2⅞″ to 9⅜″ | 21 | 2⅜″ |
| 24 blades | 15° | 6½″ | 3⅛″ to 9⅝″ | 24 | 2″ |
Plate sizes with an 18° ruler
For 20 blades and a 3″ open center in the middle:
| Plate across | Blade length | Strip | Ruler’s lines | Strips for 20 blades |
|---|---|---|---|---|
| 10″ | 3½″ | 4″ | 2⅞″ to 6⅞″ | 1 |
| 12″ | 4½″ | 5″ | 2⅞″ to 7⅞″ | 1 |
| 15″ | 6″ | 6½″ | 2⅞″ to 9⅜″ | 1 |
| 18″ | 7½″ | 8″ | 2⅞″ to 10⅞″ | 2 |
| 20″ | 8½″ | 9″ | 2⅞″ to 11⅞″ | 2 |
How it’s worked out
| Each blade’s angle: 360° ÷ 20 | 18° |
|---|---|
| The plate across, finished | 15″ |
| Each blade, from the open center out | 6″ |
| The open center | 3″ |
| The strip: the blade’s length + ½″ of seams | 6½″ |
| The ruler’s line on the strip’s top edge | 2⅞″ |
| And on its bottom edge | 9⅜″ |
| Blades from a 42″ strip, turning the ruler each cut | 21 |
Why aren’t the ruler’s lines at the plate’s own measurements? A blade’s sewing lines run to the plate’s center, but its cut edges are ¼″ outside them, and those meet beyond the center. That point is where the ruler’s tip goes. So the ruler is placed further out than the blade’s finished length, by the seam and that extra step: the lines above are the nearest ⅛″ ones, and the plate sews within a hair of its size.
Pointed or flat ends
For pointed blades, fold each wide end in half, right sides together, sew ¼″ across it and turn it: the fold makes the point. Flat blades are cut the same, and their wide ends are turned under when the plate is appliquéd. The strip is the same either way: 6½″ pointed, 6½″ flat for this plate.
The center. Cover the open center with a circle a little bigger than the opening, appliquéd over the blades’ narrow ends. See appliqué for beginners.
- Dresden Plate
Dresden Plates in Quarter Inch
Quarter Inch’s block library has a Dresden Plate of 20 blades with folded points. Its cutting chart gives the blades with the 18° ruler’s lines, as on this page. No wedge ruler? It prints Template W at true size, which cuts the same blade.
Questions
Short answers.
Something else? A real person replies.
hello@quarterinch.app
What angle is a 20 blade Dresden Plate?
18°: 360° shared by 20 blades.
What angle for 16 blades?
22½°. For 12 blades it’s 30°; for 24, 15°.
How wide a strip for Dresden blades?
The blade’s finished length plus ½″: 6½″ for 6″ blades.
How many blades from one strip?
21 6″ blades from a 42″ strip with the 18° ruler, turned each cut. Longer blades give fewer.