My Favorite Ways to Trim HSTs

rimming Half Square Triangles (HSTs) using a square ruler with a 45-degree line for precise and accurate quilting results

There are many different ways to trim Half Square Triangles (HSTs), and everyone seems to have their favorite! From specialized rulers to trimming techniques, there’s a method for every quilter. You can even skip trimming altogether (if you’re super precise!). But after lots of trial and error, I’ve narrowed down my two favorite ways to trim HSTs, balancing accuracy with an enjoyable, budget-friendly process.

I’ll also list a few other popular methods at the end—feel free to explore and find what works best for you!

My Top 2 HST Trimming Methods

1. Square Ruler with a 45-Degree Line

Using a square ruler with a 45-degree line is one of the simplest, most effective ways to trim HSTs. Here’s how it works:

• Place the 45-degree line on your ruler along the seam line of the HST.

• Trim two sides to square it up.

• Rotate the HST 180 degrees, realign, and trim the remaining two sides.

This method keeps the seam centered and is incredibly accurate with a square ruler.

Supplies Needed:

• Square ruler (I use the Creative Grids 8.5” Square Ruler about 99% of the time!)

• Optional: Rotating cutting mat for added convenience.

2. Slotted Ruler for Stability and Speed

A slotted ruler offers a stable, efficient way to trim HSTs. This method minimizes fabric shifting while you cut and yields consistent results:

• Align the 45-degree line on your HST with the ruler.

• Trim the right and left sides, then rotate the block and trim the remaining sides.

I recommend using a smaller slotted ruler, as larger ones can be cumbersome. This technique is quick, effective, and great for multiple blocks.

Supplies Needed:

• Slotted ruler, such as those from Creative Grids or QuiltCut.

Why I Don’t Use Block Loc Rulers

While Block Loc rulers are popular, they’re not my preference. Since I press my seams open, Block Loc rulers don’t work well for me (they’re designed to lock onto seams pressed to the side). Plus, they’re on the pricey side. If you enjoy them and already have some, they can deliver great results, but they just aren’t my go-to choice.

Can You Trim HSTs Before Pressing?

Yes! Some rulers (this one in particular) allow you to trim HSTs before pressing, which also removes dog ears. However, I find that pressing first helps avoid minor fabric distortions, resulting in a more accurate finish.

Other HST Trimming Techniques

There are even more methods out there, including trimming HSTs by the strip, using foundation paper piecing, and more. Do you have a favorite technique? Let me know in the comments!