Quilt block resizer

Calculator

Sizes that come out clean

Every traditional block sits on a grid. A nine-patch, Ohio star, churn dash, friendship star and shoofly are three squares across; a sawtooth star is four; a bow tie is two. The finished size divided by the grid gives the size of one grid square, and every cut is built from that.

When the grid square is a whole or half inch, the cuts land on ruler lines. A 9-inch nine-patch has 3-inch squares, cut at 3½ inches. A 10-inch nine-patch has 3⅓-inch squares, which no ruler marks, so the resizer rounds and warns you. For three-grid blocks, sizes that divide by 3 (6, 9, 12, 15 inches) are easiest, and the half sizes between them (7½, 10½, 13½) also work, because their grid squares land on half inches. A churn dash also has half-width rectangles, so it is cleanest at sizes that divide by 6. Sawtooth stars get whole-inch grid squares at multiples of 4, though any whole-inch size still lands on an eighth-inch line. Bow ties work at any whole number.

Making a 12-inch Ohio star at 10 inches

Say a pattern gives a 12-inch Ohio star and you want 10-inch blocks. At 12 inches the grid square is 4 inches, so the resizer asks for two star and two background squares at 5½ inches for the point units, four background corners at 4½, a 4½ center, and point units trimmed to 4½. The block measures 12½ inches unfinished.

Type 10 and the grid square becomes 3⅓ inches, which the note under the table shows rounded to 3⅜. The resizer rounds every cut to the nearest ⅛: 4⅞ inches for the point squares and 3⅞ for the corners and center, with point units trimmed to 3⅞. It also shows the warning and suggests 9 inches instead.

The rounding is small per piece and adds up across a row. The exact cut for a corner square would be 3.83 inches; 3⅞ is 3.875. Three of them sewn in a row with two quarter-inch seams come to 3 × 3⅞ − 1 = 10⅝ inches, an eighth more than the 10½ the block should measure. That is checked by calculation, so it assumes a perfect seam. Over a row of six blocks the extra adds up to three quarters of an inch.

You have three ways out. Trim each finished block to 10½ inches, which takes a sixteenth off each outer edge; the outer squares then finish a sixteenth narrower than the center one, too small to see. Take the tool’s suggestion and make 9-inch blocks. Or enter 10½: the grid square is 3½ inches and every cut lands on a ruler line.

Trim the point units to the same size as the corner squares in every row.

Reading the cutting list

The counts are for one block. The note under the table repeats the grid and the unfinished size, which is the number to check your test block against. On the Ohio star, the last row (“Point units: make 4, trim to”) has no fabric or count because it isn’t a cut. It is the size to square the hourglass units to after sewing. The churn dash rectangles are listed long side first, so 4½ × 2½ at 12 inches means a strip 2½ inches wide cut every 4½ inches.

The squares for the Ohio star point units are 1½ inches larger than the grid square, and the half-square triangle squares in the other blocks are 1 inch larger. That is the trimming allowance, not a mistake. If your pattern cut its triangle squares exactly and you’re comparing the two lists, the resizer’s will always be a little bigger.

Changing the block size changes the quilt

A layout of 12-inch blocks, 5 across and 6 down, makes a 60 × 72-inch center. The same 30 blocks at 10 inches make 50 × 60. To keep roughly the original size you need 6 across and 7 down, 42 blocks, for 60 × 70. The how many blocks calculator does that arithmetic for any size, and StitchTested’s quilt size chart lists the standard bed and throw sizes to aim for. Sashing widths usually come down with the block; the sashing calculator handles the strip and cornerstone cuts.

The methods it assumes

• Half-square triangles, two at a time, cut to trim (finished unit plus 1 inch).
• Ohio star point units as hourglass units made from two half-square triangles, cut to trim (finished unit plus 1½ inches).
• Sawtooth star points as no-waste flying geese, four at a time.
• Bow tie knots by stitch and flip: a small square sewn across one corner of each background square.

The step-by-step piecing for each is on the block pages: Ohio star, churn dash, friendship star, shoofly, bow tie and sawtooth star. The patriotic star throw uses sawtooth stars in a full quilt.

Before you cut a whole quilt’s worth

Make one block at the new size and measure it. It should be the finished size plus half an inch. If it’s small, your seam is wide; see how to sew an accurate quarter-inch seam. Then multiply the counts by the number of blocks and check your fabric with the fabric yield calculator.

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