I was going to write about making Half-Square Triangles and the blocks using them that we have been making in our classes this month, but I got side-tracked by some of my students and a few beginners in the Facebook Groups asking about cutting and how to work out what to cut and how big it should be. I rashly offered to do some Hints and Tips on measurements and they should be appearing on the website as I get them done. In the meantime I thought I would write about analysing a block pattern and working out how to make it.

Let’s take a very simple block to start with – a Single Irish Chain. This can be broken down into units – it has 8 Half-Square Triangle (HST) units (the corners and centre) and 8 Four-Patch units around the edges; 16 units altogether makes it a Four-Patch (or Sixteen-Patch) block. Knowing this helps us to work out what size is the easiest to make – it needs to be a number divisible by 4 – if it’s not in the 4-times-table don’t attempt it; in other words do not try to make a 9 or 10 inch block but make an 8 or 12 inch one instead, it makes the arithmetic so much easier!

The Four-Patch units are made from four smaller squares. But what size squares? If you are making a 12 inch block then each unit is going to be 12 divided by 4 meaning each unit is 3 inches. Your squares in the 4-Patch units will be half that so they will be 1½ inches. These are ‘finished’ sizes so add on the seam allowance of ½ inch for squares. You will therefore need to cut 2 inch squares (or strips) for the Four-Patch units. If your block is going to be 8 inches then your units will be 2 inches which makes your little squares only 1 inch finished – 1½ inches cut. A 16 inch block on the other hand will mean units of 4 inches and little squares of 2 inches (2½ inches cut).

The same applies to the HST units. In a 12 inch (finished) block they will be 3 inches, 2 inches in an 8 inch block and 4 inches in a 16 inch block. For HST units you need to cut squares that are 7/8 inch larger than the finished size. You need a square of each of the two fabrics and these two squares will make two HST units. For your 12 inch block your squares need to be 3 and 7/8 inch; for an 8 inch block 2 and 7/8 inch and for the 16 inch block 4 and 7/8.

The 7/8 line on the ruler is the tiny one just before the next big number – so, for instance, 3 and 7/8 is the tiny line just before the 4 inch mark. Some patterns suggest you add an inch instead of 7/8 and then trim all your triangle units to the right size. If you are a perfectionist and are willing to spend an hour or so trimming 450 HST units (you’d be surprised how many there are in some quilts) then go ahead and do this; but if you are accurate in your cutting, piecing and pressing then using 7/8 will avoid all that trimming and still be accurate enough.

You will notice that the lines have a tendency to rub off at the edges of some rulers over several years of use, but the lines in the middle will still be there for a few years yet, so use them. Rulers (and mats) do wear out with use I’m afraid. And rulers break when you drop them in the street!

Another popular and simple block is Prairie Queen. This has the same units as Single Irish Chain but fewer of them, it has nine units – one simple square, four 4-patch units and four Half-Square Triangles (HST) – so is known as a Nine-Patch block. To make life easy for yourself choose a size that is divisible by 3 – for example, 6 inches, 9 inches, 12 inches or 15 inches. Again, if the number isn’t in your 3 times-table don’t use it, so no 8 inch or 10 inch blocks unless you want to give yourself a headache. A three inch block may be a little bit small but if you enjoy making miniature quilts you might want to try it. For a six inch block each unit is six divided by three – in other words two inches. You will need to cut a 2½ inch square for the centre, 1½ inch squares (or strips) for the 4-patch units and 2 and 7/8 inch squares for the HST units. For a 9 inch block those units will be 3 inches square, so cut a 3½ inch square for the centre, 2 inch squares for the 4-patch units and 3 and 7/8 for the HST units. For a 12 inch block those units will be 4 inches square, so cut a 4½ inch square for the centre, 2½ inch squares for the 4-patch units and 4 and 7/8 inch squares for the HST units.

It’s easy when you know how! Look at a block and work out what units it is made up from and how many there are. Then you can decide how big (or small) to make it. With rotary cutting instructions the standard seam allowance is ¼ inch (that’s where all those ½ inches and eighths come from) so make sure when you sew everything together that this is what you are using. Back in the days before rotary cutters we would draw our blocks out full size onto graph paper, cut the drawing apart and glue the various shapes onto card to use as templates. Doing it this way meant we didn’t have to worry about working out sensible measurements that featured on a ruler – if we wanted to make a 10 inch 4-patch or 9-patch block then we could. The line drawn on the fabric (wrong side) was the sewing line and we would cut out leaving a suitable seam allowance of around about ¼ inch.