---
title: "Quilt Block Designer with Cutting List | Loom Mosaic"
description: "Paint a quilt block with squares and half-square triangles, preview the quilt and get cutting sizes and yardage for each fabric, free in your browser."
url: https://loommosaic.cfd/
---

Free quilt block designer

# Design a quilt block, square by square

Paint a grid with solid squares and half-square triangles, see the block repeated as a whole quilt, then get cutting sizes and yardage for every fabric.

## Fabrics

Choose slot A or B, then a fabric. Squares use A; triangles put A in the corner you pick and B in the other half.

**Keyboard shortcuts**

- **← ↑ → ↓**: Move around the grid
- **Enter Space**: Paint with the brush
- **R / Shift+R**: Turn a triangle clockwise / back
- **H**: Switch square / triangle brush
- **O**: Change the triangle direction
- **X**: Swap fabrics A and B
- **P**: Pick up the fabrics of this cell
- **1–9, 0**: Fabric A is fabric 1–10 (with `Shift`: fabric B)
- **Ctrl+Z / Ctrl+Y**: Undo / redo

## Cutting list

- Grid unit **3″** finished (4 × 4)
- Squares cut **31/2″**
- Triangle squares cut **37/8″** (finished + 7/8″, two at a time)
- For **20 blocks**

| Fabric | Cut | Strips across the width | Fabric |
| --- | --- | --- | --- |
| Muslin | **40** squares 37/8″ for trianglespaired with Teal: 80 HSTs, 4 per block **80** squares 37/8″ for trianglespaired with Saffron: 160 HSTs, 8 per block **40** squares 37/8″ for trianglespaired with Indigo: 80 HSTs, 4 per block | 4 strips 37/8″ wide 8 strips 37/8″ wide 4 strips 37/8″ wide | **1 3/4 yd** 62″ of strips · 1.6 m |
| Indigo | **40** squares 37/8″ for trianglespaired with Muslin: 80 HSTs, 4 per block | 4 strips 37/8″ wide | **1/2 yd** 151/2″ of strips · 0.4 m |
| Saffron | **80** squares 37/8″ for trianglespaired with Muslin: 160 HSTs, 8 per block | 8 strips 37/8″ wide | **7/8 yd** 31″ of strips · 0.8 m |
| Teal | **40** squares 37/8″ for trianglespaired with Muslin: 80 HSTs, 4 per block | 4 strips 37/8″ wide | **1/2 yd** 151/2″ of strips · 0.4 m |

Fabric is the length of strips cut across the width, rounded up to the next 1/8 yard or 10 cm. Buy a little extra for straightening the edge and for mistakes.

## How to design a block

Pick a grid size: a 4 × 4 grid on a 12″ block gives 3″ squares, a 6 × 6 grid gives 2″ squares. Choose **Square** to paint whole squares in fabric A, or **Triangle** to paint half-square triangles (HSTs): fabric A fills the corner shown in the direction buttons and fabric B the other half. Tap a triangle again to turn it, or use **Turn**. **Pick** copies a cell's fabrics into the brush.

Edit any fabric's colour and name, add up to twelve, and remove ones you no longer need. Everything also works from the keyboard: move with the arrow keys and paint with Enter or Space.

### Preview and cutting list

The preview repeats your block across the quilt. **Block turns** rotates every other block, turns each block of a 2 × 2 group a quarter further, or mirrors neighbours, which is how many secondary patterns appear. Sashing adds strips between blocks, with cornerstones where they cross.

For the cutting list, enter the finished block size. Squares are cut at the finished size plus two seam allowances (½″ with ¼″ seams). Triangles are made two at a time from a pair of squares cut 7/8″ larger than the finished size; choose the oversized option to cut 1″ larger and trim each unit to size. Fabric is worked out as strips across the usable width (42″ by default, the width of quilting cotton once the selvages are trimmed).

### Worked example

The Sawtooth Star starter at 12″ finished has 3″ units. Each block needs four 3½″ background squares, four 3½″ centre squares (or one 6½″ square cut as a single piece) and eight HSTs from four pairs of 3 7/8″ squares. Twenty blocks need 80 background squares; twelve fit across a 42″ strip, so you cut seven strips.

## Sources

- Utah State University Extension, [Half Square Triangles, Broken Dishes Block, Pinwheel Block](https://extension.usu.edu/sewing/research/half-square-triangles-broken-dishes-block-pinwheel-block): add 7/8″ to the finished size for two-at-a-time HSTs, and a 3″ finished unit measures 3½″ before it is sewn in.
- Missouri Star Quilt Co., [How to figure yardage for quilt backing](https://www.missouriquiltco.com/blogs/missouri-star-blog/how-to-figure-yardage-for-quilt-backing): standard quilting cotton is about 42″ wide with about 40″ usable once the selvages are trimmed.
- Nebraska Quilt Company, [How to calculate longarm backing fabric](https://www.nebraskaquiltcompany.com/blogs/welcome-to-nqc/how-to-calculate-longarm-backing-fabric-6-step-guide-2026): 44″ fabric is typically 40″ to 42″ usable after removing the selvages.
- The four- and eight-at-a-time sizes on the [HST calculator](https://loommosaic.cfd/half-square-triangle-calculator/) are worked out from the same geometry, shown on that page.

## Quilting calculators

From the size of the quilt to the last strip of binding.

- [Quilt size calculator](https://loommosaic.cfd/quilt-size-calculator/): Finished size for any bed from drop and pillow tuck, then blocks across and down, sashing and borders.
- [Half-square triangle calculator](https://loommosaic.cfd/half-square-triangle-calculator/): Square sizes for two, four and eight HSTs at a time, in inches and centimetres, with fabric needed.
- [Binding calculator](https://loommosaic.cfd/quilt-binding-calculator/): Strips to cut across the width of fabric and how much fabric to buy for straight-grain binding.
- [Backing calculator](https://loommosaic.cfd/quilt-backing-calculator/): How many widths to join, which way the seams run and the yardage, with extra for longarm quilting.

## Recommended

Two free tools from outside the quilting room that come in handy when you shop for fabric online.

### CleanTempMail

Fabric shops often ask for an email address before a free pattern download or a welcome discount. A disposable inbox from CleanTempMail needs no sign-up and receives the email straight away, and everything in it is deleted after three days, so the follow-up newsletters never reach your own inbox.

[Get a temporary email address](https://cleantempmail.com/)

### WebTraceCheck

Found a fat-quarter bundle priced well below everywhere else, on a shop you have never heard of? WebTraceCheck can look up the shop's domain and check its security headers, or open the site in a disposable cloud browser that is wiped after the session, before you type in any card details.

[Check a shop with WebTraceCheck](https://webtracecheck.com/)

## Questions about the block designer

**How do I paint a half-square triangle?**

Choose the Triangle brush, pick fabrics A and B, and choose which corner fabric A should fill with the four direction buttons. Click or tap a square to paint it. Tapping the same triangle again turns it a quarter turn, which is often quicker than changing the direction first.

**Why are triangle squares cut 7/8″ bigger, but plain squares only 1/2″?**

A plain square needs a 1/4″ seam allowance on each side, so 1/2″ in total. For a half-square triangle, two squares are sewn together along the diagonal and then cut apart, and the diagonal seam takes up extra fabric: with 1/4″ seams the triangle legs must be about 0.854″ longer than the finished size, which quilters round up to 7/8″.

**Can I use the designer without a mouse?**

Yes. Tab into the grid, move with the arrow keys and press Enter or Space to paint. R turns a triangle, H switches between the square and triangle brush, O changes the triangle direction, X swaps fabrics A and B, and the number keys choose a fabric. Ctrl+Z and Ctrl+Y undo and redo.

**Where are my blocks saved?**

In your browser's local storage on this device. Nothing is uploaded. The current block is kept automatically, and Save block adds it to My blocks. Clearing your browser data removes them, so download a design file for anything you want to keep.

**Does the cutting list combine squares into bigger pieces?**

No. It lists one piece per grid square, which always sews together in straight rows. Where several squares of the same fabric sit together, such as the centre of a star, you can cut one larger piece instead: its finished size plus 1/2″.

**How is the fabric amount worked out?**

Each size of piece is cut from strips across the usable width of fabric. The calculator counts how many pieces fit in one strip, how many strips that takes, and adds up the strip widths. It does not include binding, backing, borders or spare fabric for mistakes.