How to Make Quarter Square Triangles: Three Methods and a Size Chart

A quarter square triangle is one square divided on both diagonals. Four triangles, one unit, and the whole thing rests on a single number: cut the squares you start with at the finished size plus 1 1/4 inches.

That number, and the three ways of getting there, is what this tutorial is. There is a quarter square triangle size chart below, a free printable version of it at the end, and Yvonne showing both of the sewn methods on our own sewing machine.

What a quarter square triangle unit is

Before the tutorial proper, the shape itself, because half the trouble people have with QST blocks comes from not being sure what they are looking at. It is one of the two units that most of pieced quilting is built on, and it is the one that gets skipped.

A quarter square triangle is created by dividing a square on both diagonals. Each of the four triangles has two equal sides and one right angle. The long side of each one sits on the outside of the unit and the two short sides run in to the center, so the seams inside the unit are two straight lines crossing in the middle.

Made from two fabrics, with the matching pair opposite each other, the unit reads as an hourglass, and that is what most quilters call it: an hourglass unit, or an hourglass quilt block when it is used on its own across a whole quilt. You will see it written hour glass block as two words about as often as one. Made from four fabrics it reads as a small pinwheel of triangles instead. The construction is identical either way, and so is the quilt math behind it.

The unit earns its place because of what it partners with. Quarter square triangle units look well on their own in a quilt, and they go with half square triangles, a solid square here and there, and rectangles to build a long list of quilt blocks, the Ohio Star among them, along with Milky Way and Handy Andy. Change which triangle is which fabric and secondary patterns appear across the quilt that are in none of the blocks on their own.

The quarter square triangle size chart

One number does all the work. Cut the squares at the finished size plus 1 1/4 inches. That holds for every method below, which is what makes this unit easier than it looks.

Finished is what the unit measures inside the quilt. Trim to is the unfinished size, what it measures before it is sewn to anything, always the finished size plus 1/2 inch. Starting squares are the squares you cut before any sewing happens, and they are the only thing the chart really has to tell you. However you make them, you get as many units as the number of squares you started with: two squares give two units, four squares give four.

All measurements in inches. If you want the quarter square triangle math rather than the chart: finished size plus 1 1/4 inches for the starting squares, finished size plus 1/2 inch for the unfinished size you trim to. No calculator needed, and any size you like fits between the rows. It is the least demanding quilt math in patchwork, which is a relief on a unit that looks this complicated.

It is worth putting the two units side by side. A half square triangle is the finished size plus 7/8 inch. A quarter square triangle is the finished size plus 1 1/4 inches. The extra 3/8 inch is the second seam, because this unit crosses the square twice where the half square triangle crosses it once. That is the entire difference in the arithmetic, and it is the number people get wrong when they work from memory.

Straight from a precut, a 5 inch charm square gives a unit that finishes at 3 3/4 inches and trims to 4 1/4. A 10 inch layer cake square gives one that finishes at 8 3/4 and trims to 9 1/4.

Method one: quarter square triangles from two fabrics

This is the quarter square triangle tutorial most quilters want, so it comes first.

This is the method to learn first, and the one Yvonne uses in the video tutorial above. It starts with half square triangles and turns them into quarter square triangles with a second pass under the needle. Four lines drawn, four seams sewn, two cuts, and the quilting part of it is over.

Take two starting squares at the chart size, one light and one dark, and put them right sides together. Draw a diagonal line on the wrong side of the lighter one, from one corner to the opposite corner, and sew a quarter inch either side of that drawn line.

Cut on the drawn line with a rotary cutter or a pair of scissors. Set the seam first, then press towards the darker fabric, catching the corner of the iron in the seam and moving up the straight grain rather than along the diagonal seam. That seam is on the bias, and pressing along it is how you end up with a wonky unit. You now have two half square triangle units, and if that step is new, our guide to making half square triangles has three ways of doing it and a size chart of its own.

Now put the two half square triangles right sides together, the dark of one against the light of the other. Because both were pressed towards the dark, the seams nest, and you can feel them lock with your fingers rather than pinning. Draw a diagonal line across the top one running the opposite way to the diagonal seam underneath, and sew a quarter inch either side of it.

Cut on that line and open them out. Two QSTs, and the points in the middle should meet exactly, because the nested seam held them there while you sewed. Two squares in, two QST blocks out.

Method two: quarter square triangles from four fabrics

The steps in this half of the tutorial are the same. What changes is that you start with four squares instead of two, and you re-pair across the pairs.

Pair the four starting squares up however you like, right sides together, and make four half square triangle units, two of each pairing. Press them all towards the darker side so they will nest. Then put one unit from the first pairing against one from the second, seams nesting, draw the other diagonal, sew either side and cut. Do the same with the remaining two.

Four units from four squares. There is one thing to know before you cut for a pattern: two of them come out as mirror images of the other two, because they are opposite halves of the same pair. If the block you are making needs them all identical, make twice as many as you need and use the half that match. Yvonne says this plainly in the video, and it is the single thing that catches people out with the four fabric version.

Method three: cutting the four triangles and sewing them

The oldest route in quilting, and the one the pattern books use, skips the half square triangle stage entirely. Cut a square at the chart size and cut it in half diagonally twice, corner to corner and then corner to corner again, which creates four triangles. Do that to a second square in another fabric, and you have the eight triangles for two hourglass units.

Sew them in pairs first, then join the two halves across the middle, matching the center point where the seams cross. It uses less fabric than the sewn methods and it is how a cutting list in a pattern will usually be written, with a square marked to be cut in half diagonally twice.

The catch is bias edges. Cutting a square on both diagonals puts the straight grain on the long side of each triangle and the bias on the two short sides, and those short sides are the ones that get sewn. The unit ends up perfectly stable, since the straight grain finishes on the outside, but it is stretchy while you are handling it. That is why the sewn methods are the ones most quilters reach for now, and why this one is worth knowing anyway: sometimes a pattern hands you the triangles already cut.

Spinning the center seam so the unit lies flat

Four seams meet at the center of this unit. Press that center seam to one side in the ordinary way and all of them stack in the same place, so the middle sits up in a hard little knot that shows through the quilting later. Pressing the seams open is one answer, and plenty of quilters do press open here for exactly that reason, but it costs you the nesting that made the points match. There is a better one.

Spin it instead. Turn the unit over, find the two or three stitches running through the seam allowance itself right at the center, and unpick them as far as the stitching line and no further, so the stitching line itself stays intact. The allowances are then free to turn. Give them a twist with your thumbs so they all run the same way round the middle, finger press, then set the iron down and follow that circle. A tiny four patch appears on the back and the middle flattens out completely.

It is the same trick that flattens a Pinwheel block, and it takes about ten seconds once you have done it twice.

Trimming to size, without losing the middle

Every unit comes off the machine slightly oversized on purpose, and it gets trimmed before it goes anywhere near a block. The difficulty is that trimming from one corner and then the opposite corner pushes the center off center, which is the one thing this unit cannot survive. Line the ruler up on the middle instead of on a corner.

So work from the middle out. Put the 45 degree lines of a square ruler along the two seams, and put the mark for half your desired size on the center point where the four seams meet. For a 3 1/2 inch trim that mark is 1 3/4. Cut the two sides that stick out, turn the unit round, line the cut edges up on the full trim size, and cut the other two straight edges. The center stays where it belongs, and every QST in the batch comes out the same size.

A square ruler in the size you use most is the tool that makes this quick, and a 12 1/2 inch square is the one worth owning first because it handles a whole quilt block as well. A rotating cutting mat is the other thing that helps, because it lets you turn the unit without lifting it. There are also quarter square triangle rulers made for the job, but none of them is necessary if you have a square with a 45 degree line on it.

Look at the blade in your rotary cutter before a stack of units, too. A blade that has gone dull drags instead of slicing, and on a unit with four bias edges meeting in the middle that drag moves the fabric. A fresh rotary blade is a cheaper fix than recutting.

Where the grain sits, and why these behave

Fabric is woven with lengthwise warp threads and crosswise weft threads, both of them firm. At 45 degrees to those lies the bias, which has the least strength and the most stretch, and the old quilting rule is that when in doubt you want the straight grain on the outside edges.

A quarter square triangle unit obliges. Whichever of the three methods you use, the four outer edges of the finished unit end up on the straight grain and the bias is buried in the seams. That is why a unit that feels alarmingly stretchy while you are making it is perfectly well behaved once it is trimmed, and why these sit so calmly next to plain squares in a block.

Quarter square triangle blocks worth making

Quarter square triangle blocks turn up all over quilting, on their own and inside larger quilt blocks.

Four of these units with a plain corner square at each corner and a solid square in the middle give the Ohio Star, which is the classic use and the reason most quilters meet the unit at all. The Ohio Star is where the background fabric starts to matter, because it is what the star points are read against.

On their own, set edge to edge across a quilt top, hourglass blocks make an hourglass quilt. It is one of the simplest quilt patterns in quilting and one of the best for showing off a fabric collection, because every unit holds two fabrics and the eye reads the light triangles as a lattice running corner to corner through the quilt. It is a forgiving quilt to machine quilt, too, because the seam lines give you something to follow.

Run a single row of them along the edge of a quilt and you have an hourglass border, which is a good use for fabric scraps and for the leftovers from a block quilt.

And if you want the same idea with half the seams, the Pinwheel and the Friendship Star are both built from half square triangles instead, and both are a rung easier than anything with a quarter square triangle in it.

The free quarter square triangle size chart

Everything above fits on one page, and we have put it there so it can live next to the machine instead of on a phone.

The sheet has the size chart, the formula, both sewn methods step by step as a tutorial in miniature, how to spin the middle and how to trim without moving the center. It prints on letter or A4, and it is a cheat sheet rather than a pattern, so nothing on it needs to print at actual size.

The downloadable PDF is here: the quarter square triangle size chart. It is free to print, use and teach.

Quarter square triangle questions we are asked most

What size are the starting squares for a quarter square triangle?

The finished size plus 1 1/4 inches. For a unit that finishes at 4 inches, cut squares at 5 1/4 and trim the finished units to 4 1/2. The chart above covers the sizes that come up most, and the formula covers the rest.

What is the difference between a half square triangle and a quarter square triangle?

A half square triangle is a square split once, so it holds two triangles and you cut at the finished size plus 7/8 inch. A quarter square triangle is a square split on both diagonals, so it holds four triangles and you cut at the finished size plus 1 1/4 inches. The extra 3/8 inch pays for the second seam.

Is a quarter square triangle the same as an hourglass block?

An hourglass is what a quarter square triangle unit is called when it is made from two fabrics, because the matching pair opposite each other reads as an hourglass shape. Same unit, same measurements. Made from four fabrics nobody calls it an hourglass, because it no longer looks like one.

Why is the middle of my unit lumpy?

Because four seam allowances are stacked in one place. Unpick the two or three stitches through the allowance at the very center, twist the allowances so they turn in a circle, and press again. Nothing else about the unit needs redoing.

Is this a good unit for a beginner in quilting?

It is a fair second step. Make half square triangles first, because this tutorial starts with two of them, and then this unit is one more seam and one more cut. Nothing in it needs a special tool, and the quilting itself is four straight lines of stitching.

How do I make quarter square triangles from a charm pack?

Two 5 inch charm squares give two units that finish at 3 3/4 inches and trim to 4 1/4. Four charms give four units. It is the fastest way to try the method without cutting into yardage.

Should I press the seams open on a QST?

You can, and it gives the flattest unit, but you lose the nesting that makes the points meet. Spinning the center seam gets you a flat middle without giving that up, so press seams towards the dark, then spin. If a pattern you are following asks you to press open, do what it says, and pin the center point instead.

Do I need a special quarter square triangle ruler?

No. A square ruler with a 45 degree line does everything, and it is more useful the rest of the time. The specialist rulers save a step if you make a great many of these, and nothing more.

Why do two of my four fabric units come out different?

Because they are opposite halves of the same pairing, so the order of the colors reverses. That is normal. If a block needs them all identical, make twice as many as you need and use the matching half.

What to have ready

• Two fabrics for an hourglass, or four for the four fabric version. Charm packs are the easiest way to start, and fabric by the yard is what the background should come from once you are making a quilt of them.
• A rotary cutter with a sharp blade, a mat, and a square ruler with a 45 degree line for trimming.
• Something that keeps the 1/4 inch honest on every seam, such as our seam guide ruler.
• A marking pen or pencil for the diagonal lines, pins, and a seam ripper for spinning the middle, all in notions.
• An iron, and the patience to press rather than push.
• The size chart above, printed.

Where to start

Take two 5 inch charm squares, one light and one dark, and follow the first method in this tutorial to make two units. Spin the middles. Trim them to 4 1/4 inches with the ruler mark at 2 1/8 on the center point.

Then measure them. If they are square and the points meet in the middle, every size in the chart will behave, and you have learned the unit that the Ohio Star and every other hourglass quilt block is built from. That is the whole tutorial in two squares.

Marbelia Fernandes
The Fabric Hut Co-Founder

P.S. If you only remember one thing from this page, make it 1 1/4. Seven eighths for half square triangles, one and a quarter for these.