The shirts are the fabric and the memory, so the math starts with how many you have, or how big a quilt you owe. Both directions work here, with the cut size that fits most prints and the stabilizer that keeps knit shirts behaving.
Shirts and Size
Your Quilt
64 × 80in
4 × 5 grid of 14″ blocks
Rough-cut each shirt front, fuse interfacing to the back, then square to 14″ with the print centered.
- Blocks finish13.5″ + 2″ sashing
- Fusible interfacing (20″)5 ½ yd
- Sashing fabric, about1 ⅜ yd
- Backing at 4″ overhang72 × 88 in
The Formulas
grid = the factor pair of your shirt count nearest 3:4 · quilt = grid × (block finished + sashing) + sashingstabilizer = shirts × (cut size)² ÷ (20 in × 36) yards of fusibleT-shirt knit stretches; lightweight fusible interfacing ironed to the back of every block, and the knit then handles like quilting cotton. Buy it by the yard off the 20 in bolt and cut it to the block.
Worked Example
Twenty shirts, cut 14 in, with 2 in sashing:
- Grid: 4 × 5. Finished blocks 13½ + sashing: quilt about 64 × 80 in: a generous throw.
- Stabilizer: 20 × 14² = 3,920 sq in ÷ 720 → 5½ yd of 20 in fusible.
- Plus sashing fabric (about 1¾ yd) and the usual backing, batting, and binding, the linked calculators price those.
Shirts by Quilt Size
14 in blocks with 2 in sashing, computed by the calculator above.
| Quilt | Grid | Shirts |
|---|---|---|
| Lap · 49 × 64 in | 3 × 4 | 12 |
| Throw · 64 × 80 in | 4 × 5 | 20 |
| Twin · 80 × 95 in | 5 × 6 | 30 |
| Full · 95 × 95 in | 6 × 6 | 36 |
Preparing the Shirts
- Rough-cut first: slice each shirt up the sides, keep the printed front panel whole, and fuse interfacing to the back before the final square-up cut.
- Center the print, not the shirt: the cut square frames the design, and pockets or small crests can share a block.
- Mixed print sizes: keep one cut size and float small prints in their square: mixed block sizes turn the layout into a puzzle commission (price accordingly).
Assumptions and Defaults
- Blocks finish at cut − ½; sashing frames between and around.
- Stabilizer assumes 20 in usable fusible; 44 in interfacing halves the yardage.
- Grid choice prefers longer-than-wide (bed-shaped) factor pairs, with spares noted.
T-Shirt Quilt Questions, Answered
How many T-shirts do I need for a quilt?
A T-shirt quilt needs about twelve shirts for a lap quilt in a 3 × 4 grid, twenty for a large throw, and thirty for a twin, at 14 in blocks with sashing. The chart lists these sizes, and the calculator works the other way from your exact shirt count.
What size do I cut T-shirt quilt blocks?
T-shirt quilt blocks are usually cut 14 to 15 in, which fits most adult shirt prints with a margin, while 12 in suits youth shirts. Use one block size for the whole quilt, and measure your largest print first so it sets the size.
Do I really need interfacing for a T-shirt quilt?
Yes, a T-shirt quilt needs interfacing, because knit fabric stretches as you sew, and without support the quilt ripples for good. Lightweight fusible tricot keeps the shirts soft, and if you iron it on before the final cut, the blocks handle like woven cotton.
Can I use the backs and sleeves of the T-shirts too?
Yes, printed shirt backs make blocks just like the fronts, and plain backs can become cornerstones or filler blocks when you are short of shirts. A 17-shirt quilt, for example, can become a 4 × 5 layout with three plain blocks carrying embroidered dates.