Why Make Your Own bias strips instead of buying bias tape?
I just want to point out that if you desire, you can purchase pre-folded bias tape. It is typically sold online often in polyester (or a blend of polyester and cotton). I prefer to match my neckline finish exactly with the fabric I am sewing the garment with, so making my own bias strips is just a personal preference (personal preference comes into play a lot with sewing). Making my own bias strips is also effort to utilize fabric that is often leftover so it does not go to waste (it is a great hack for using excess fabric on future projects too). Another thing to note is there are bias tape "makers" that will prefold your fabric. These can be great in some cases but with certain light weigth textiles such as linen and linen/cotton blends they can be a tad tricky. The method I use to apply does not require you to own or master the art of making bias strips. If you are curious to purchase one, you can readily find them online (I use an 18 mm bias tape maker for double fold tapes which essentially replicates the look of the results of my bias neckline facings). Scroll to end of tutorial to learn how to make bias tape with a bias tape maker.
Preparing Bias Strips
Your pattern may leave excess space for creating a stash of bias strips/tape. This is a great way to utilize excess fabric. The Third Born Simple Box Top will have a decent sized square for you to utilize to make your own bias strips. Cut strips on the true bias (45 degrees from the selvage) by using a clear ruler to draw 1 inch parallel lines with a pen (or desired width). "FriXion Pens" are a great option as they erase with heat from an iron. You can easily order FriXion pens online or find them in the "office" section of your department store.
When making bias strips out of a scrap of fabric such as pictured below, you will usually need to connect two pieces of bias strips to get the length you need. To determine how much you need measure around the circumference of your armhole/neckline to get an estimate (add a few extra inches onto your measurement to make sure you have enough). I usually try to make about 25-30'' strips (sufficient for most crew necks and arm holes).
Combine two bias strips to make final strip about 25-30'' long (25'' is plenty for simple box top neckline sizes xs-xxl). You may need a bit more for v-neck patterns and armholes depending on the pattern (just do a quick measure with measuring tape to check.
Attaching strips at an angle will prevent bulk (if on a straight line the seam will fold on top of itself). If you are more comfortable sewing together on a straight edge that is okay to do so, it is just something to consider.
Notice the edges overhang: if you align tips it will not work out correctly.
Stitch together 1/4'' seam allowance:
Press apart and trim corners sticking out.
Your 1'' bias strip is ready to apply to your neckline.
Visit "Bias Facings for Necklines and Armholes" to learn how to apply to neckline.