Quick answer: how to calculate a t-shirt quilt
Use the T-Shirt Quilt Calculator with your own t-shirts available, panels across and panel cut size, to check finished panel size, rows needed, total panels, blank panels, finished quilt size and interfacing pieces needed before you cut.
A t-shirt quilt is made from square panels cut from t-shirts, stabilised with fusible interfacing, then sewn together like quilt blocks. Each panel needs one interfacing piece the same cut size as the panel.
Finished panel size equals panel cut size minus 0.5 inch, because seam allowance is 0.25 inch on each side. Rows needed equals t-shirts available divided by panels across, rounded up to a whole number. Total panels in layout equals panels across times rows needed. Blank panels needed equals total panels in layout minus t-shirts available.
For example, 24 t-shirts, 6 panels across, panel cut size 14.5 inches, give finished panel size 14 inches, 4 rows, 24 panels total, 0 blank panels, a finished quilt 84 by 56 inches, and 24 interfacing pieces.
How to calculate a t-shirt quilt
What you need to measure
You need three inputs: t-shirts available, panels across, and panel cut size. T-shirts available is a whole number, greater than zero, counted as one panel per shirt unless a shirt gives two usable panels, which is covered under variations below. Panels across is a whole number, greater than zero, counted across one row of the quilt. Panel cut size is the size of one square panel before sewing, in inches or centimetres, not the finished panel size. Seam allowance is fixed at 0.25 inch on each side, as is standard for piecing, so you do not enter a seam allowance separately.
Formula and calculation rule
Finished panel size equals panel cut size minus 0.5 inch, because seam allowance is 0.25 inch on each side, and 0.25 plus 0.25 equals 0.5. Rows needed equals t-shirts available divided by panels across, rounded up to a whole number, because a partial row cannot be sewn as a full row, and the layout must hold every panel. Total panels in layout equals panels across times rows needed. Blank panels needed equals total panels in layout minus t-shirts available, and blank panels are filled with plain fabric panels, not with t-shirt panels. Finished quilt width equals panels across times finished panel size. Finished quilt length equals rows needed times finished panel size. Interfacing pieces needed equals t-shirts available times 1, because each panel needs one interfacing piece the same cut size as the panel.
Step by step example
Take t-shirts available 18, panels across 4, panel cut size 16.5 inches.
Finished panel size: 16.5 minus 0.5 equals 16 inches.
Rows needed: 18 divided by 4 equals 4.5, rounded up to a whole number, which is 5 rows.
Total panels in layout: 4 times 5 equals 20 panels. Blank panels needed: 20 minus 18 equals 2 blank panels.
Finished quilt width: 4 times 16 equals 64 inches. Finished quilt length: 5 times 16 equals 80 inches.
Interfacing pieces needed: 18 times 1 equals 18 interfacing pieces, one per t-shirt panel, each the same cut size as the panel, which is 16.5 inches square.
T-shirt quilt panel size chart
This chart uses seam allowance 0.25 inch on each side, as is standard for piecing. Finished panel size equals panel cut size minus 0.5 inch, because 0.25 plus 0.25 equals 0.5.
| Panel cut size | Finished panel size |
|---|---|
| 12.5 inches | 12 inches |
| 14.5 inches | 14 inches |
| 16.5 inches | 16 inches |
Use this chart for the panel cut sizes shown. For another panel cut size, use the calculator above, with the same formula: finished panel size equals panel cut size minus 0.5 inch.
Important variations and exceptions
- Count panels, not shirts, if a shirt gives two usable panels. The formulas count one panel per shirt. If a shirt gives two usable panels, count panels, not shirts, and work rows needed, total panels and blank panels from the panel count, because rows needed comes from panels divided by panels across, not from shirts alone. In that case, interfacing pieces follow the panel count too, with one interfacing piece per panel.
- Sashing is not included. This calculation joins panels directly, like quilt blocks, with no sashing between panels. If sashing is wanted between panels, finished quilt size will be larger, and strip counts will be different, so use the Sashing Calculator for sashing after the panel layout is worked out.
- Backing and batting are separate calculations. This calculation gives panel layout, finished quilt size and interfacing pieces only. Backing size and yardage come from the Backing Calculator, and batting size and yardage come from the Batting Calculator, using the finished quilt size from this calculation.
- Finished size is after sewing, before washing. Finished panel size and finished quilt size are sizes after sewing, before washing. Washing may change a t-shirt quilt slightly, because t-shirt fabric is stretchy, but washing is not part of this calculation, so do not add or subtract anything for washing when you check finished quilt size.
- Interfacing choice does not change finished panel size. Interfacing choice, light, medium, or fusible, does not change the finished panel size in this calculation, because finished panel size comes from panel cut size and seam allowance only. Interfacing only stabilises the stretchy t-shirt fabric, so panels hold their shape while they are cut and sewn.
Design fit is separate from panel math
Panel math tells you the panel size, not whether a design fits inside it. Measure the largest design first, then choose a finished block larger than that design, with margin beyond the seam allowance. For example, a 13 inch wide print needs at least a 14 inch finished block, which means a 14.5 inch cut block at the fixed 0.25 inch seam allowance per side. The design, not the shirt seams, decides the block, so centre the design with a square ruler before you trim. Cutting everything to one block size is the easiest route, and it accepts more blank margin around small designs. Mixed block sizes are possible, but they need a shared grid plan, and they are not covered by this calculator, which uses one square panel size for the whole layout.
Common finished block sizes run from 12 to 16 inches, with 10 inches for kids shirts and 18 inches as an option for very large prints. Do not treat one most common size as settled, because the pages read disagree: one calculator calls 14 inches most common for adult shirts, another calls 15 inches most common because it fits adult prints. Pick the size your largest design actually needs, not a most common label.
Panels, shirts, and the grid are three different counts
The calculator counts panels from a grid: rows times panels across. Its t-shirts available input assumes one panel per shirt, unless you count panels yourself. If a shirt gives two usable panels, front and back, count panels, not shirts, and the shirt count for the same grid can halve: 20 panels can come from 10 two sided shirts, or from 20 one sided shirts. Blank panels are grid slots with no t-shirt panel, filled with plain fabric, a pocket, a sleeve logo, or a photo or embroidered block. They are not a mistake, they are what happens when the panel count is not an exact multiple of panels across.
Never publish a single shirt count for a named quilt size without its assumptions. Queen shows why. With 14 inch blocks and sashing plus an outer frame, 30 shirts can make an 82 by 98 inch top, and 36 shirts can make a 98 by 98 inch queen. With 15 inch blocks, 2 inch sashing and a 3 inch border, 30 shirts can make an 89 by 106 inch queen. As service ranges with no block or sashing model stated, queen is also given as 40 to 48 shirts for a 99 by 99 inch quilt, and as 50 to 60 shirts for a 92 by 100 inch quilt. Those are not arithmetic errors, they are different block sizes, sashing models, borders, and shirt sides. State block size, sashing model, border, and one sided or two sided shirts beside every count you quote.
Sashing has two models, and this tool has neither
State this plainly, because readers comparing this tool with other calculators will otherwise expect a larger finished quilt. This calculator joins panels directly, with no sashing and no border, so its finished size is panels across times finished panel, by rows times finished panel. If you add sashing afterwards, use the model that matches what you actually sew, because the two models give different sizes from the same grid.
Model A, sashing between blocks only: width equals panels across times finished panel, plus panels across minus 1, times sashing width. Length equals rows times finished panel, plus rows minus 1, times sashing width. Model B, sashing between blocks plus a matching outer frame at the same width: width equals panels across times finished panel, plus panels across plus 1, times sashing width. Length equals rows times finished panel, plus rows plus 1, times sashing width. A separate border is a third addition, added twice, once on each side, on top of whichever sashing model you use.
| Same 4 by 5 grid, 14 inch finished panels, 2 inch sashing | Finished width | Finished length |
|---|---|---|
| No sashing, this tool | 56 inches | 70 inches |
| Between blocks only | 62 inches | 78 inches |
| Between blocks plus outer frame | 66 inches | 82 inches |
For comparison, a different model with different inputs gives a different size again: 4 by 5 grid, 15 inch finished panels, 2 inch sashing between blocks only, plus a 3 inch border, gives 72 by 89 inches. Width is 60 plus 6 plus 6, which is 72. Length is 75 plus 8 plus 6, which is 89. Never compare finished sizes across pages without checking block size, sashing model, and border first.
Interfacing: fuse before you cut, count one per panel
Knit stretches too much without stabilising, so fuse a lightweight woven fusible interfacing to the back of every panel before cutting to final size, and wash shirts without fabric softener first. The pages read name Pellon SF101 for this step. The calculator counts one interfacing piece per panel, at the panel cut size. Other pages cut interfacing oversize first and then trim panel and interfacing together to cut size, but they disagree on the oversize amount, so this guide does not copy any one interfacing yardage figure from them. The count stays one per panel either way, only the starting cut size before trimming differs. A fleece or minky back with no batting is an alternative construction mentioned on one page, not the default, and backing and batting margins, where given, are about 8 inches in total in each dimension, or 4 inches on every side, which you must allow separately from the panel finished size.
How to make sure your result is correct
- Check cut size, not finished size, as the input. Panel cut size is the size before sewing. Using finished panel size as the input subtracts the seam allowance twice, once in your input and once in the formula, and gives a finished panel size too small by 0.5 inch.
- Check seam allowance on both sides. Finished panel size equals panel cut size minus 0.5 inch, not minus 0.25 inch once, because each side of a panel loses one seam allowance of 0.25 inch where it joins the next panel.
- Check rows rounding up and blank panels. Rows needed is rounded up to a whole number, so total panels in layout may be more than t-shirts available, and the difference is blank panels needed. Blank panels are expected when t-shirts available is not an exact multiple of panels across, not a mistake. For example, 18 t-shirts with 4 panels across give 5 rows, 20 panels total, and 2 blank panels.
- Check units. T-shirts available, panels across and panel cut size must be used in the same unit system, inches or centimetres. In centimetre mode, 1 inch equals 2.54 centimetres, so a seam allowance of 0.25 inch on each side equals 0.5 inch total, and panel cut size and finished panel size must both be in centimetres.
- Check interfacing count against panels. Interfacing pieces needed equals t-shirts available times 1, with one interfacing piece per panel, each the same cut size as the panel. Forgetting interfacing undercounts the pieces to cut, because each panel needs its own interfacing piece, not one interfacing piece for the whole quilt.
Try it with the calculator: Use the T-Shirt Quilt Calculator with your own t-shirts available, panels across and panel cut size. It uses the same steps as this guide, and it shows finished panel size, rows needed, total panels, blank panels, finished quilt size and interfacing pieces needed, together.
Worked example: 24 t-shirts, 6 panels across, panel cut size 14.5 inches
This worked example is different from the tool page example, which uses t-shirts 20, panels across 5, panel cut size 12.5 inches, finished panel size 12 inches, rows 4, total panels 20, blank panels 0, finished quilt 60 by 48 inches, and interfacing pieces 20.
Finished panel size: 14.5 minus 0.5 equals 14 inches.
Rows needed: 24 divided by 6 equals 4 rows, with no rounding up needed, because 24 is an exact multiple of 6.
Total panels in layout: 6 times 4 equals 24 panels. Blank panels needed: 24 minus 24 equals 0 blank panels.
Finished quilt width: 6 times 14 equals 84 inches. Finished quilt length: 4 times 14 equals 56 inches.
Interfacing pieces needed: 24 times 1 equals 24 interfacing pieces, one per t-shirt panel, each the same cut size as the panel, which is 14.5 inches square.
Frequently asked questions
A t-shirt quilt is made from square panels cut from t-shirts, stabilised with fusible interfacing, then sewn together like quilt blocks. Each panel needs one interfacing piece the same cut size as the panel, because interfacing stabilises the stretchy t-shirt fabric.
Finished panel size equals panel cut size minus 0.5 inch, because seam allowance is 0.25 inch on each side, and 0.25 plus 0.25 equals 0.5. For example, panel cut size 14.5 inches gives finished panel size 14.5 minus 0.5, which is 14 inches.
Rows needed equals t-shirts available divided by panels across, rounded up to a whole number. Total panels in layout equals panels across times rows needed. Blank panels needed equals total panels in layout minus t-shirts available. For example, 24 t-shirts with 6 panels across give 4 rows, 24 panels total, and 0 blank panels.
Yes. Each panel needs one interfacing piece the same cut size as the panel. Interfacing pieces needed equals t-shirts available times 1, with one panel per shirt. For example, 24 t-shirts need 24 interfacing pieces.
Sashing is not included in this calculation, which joins panels directly, like quilt blocks. If sashing is wanted between panels, finished quilt size will be larger, and strip counts will be different, so use the Sashing Calculator for sashing after the panel layout is worked out.
Related guides and calculators
Use the T-Shirt Quilt Calculator for your own t-shirts available, panels across and panel cut size. For quilt size by bed, use the Quilt Size Calculator, for block layout, use the Block Size Calculator, for sashing between panels, use the Sashing Calculator, for fabric yardage, use the Fabric Calculator, and for counting pieces from yardage you already own, use the Piece Count Calculator.