Sewing border strips without measuring is a recipe for disaster. Your quilt will NOT be square and may even have ripples along the edges. You spent a long time making your quilt. Be sure to take the little extra time to finish it correctly.
Your first step is to be sure that the quilt edges are square. With pieced blocks, this will be true because you have squared each unit as you went along (didn't you?). Some quilts are made of long strips or other types of joined units, such as Bargello. With these, the edges may be quite uneven.
Lay the quilt out on a flat surface with your cutting mat under one corner. Use a square ruler, the largest one you own, and put it in the corner. You must use a little judgment, possibly adding your long rotary ruler to the ends to be sure you will be able to continue the line you are trimming all the way down the side of the quilt. It is possibly (although not likely) that the side of the quilt bows further in than the ends (concave). You need to trim so that all the sides are straight, the corners make right angles and the quilt, when folded, will meet exactly in the four corners.
Note: You may wish to block your quilt before trimming. If you feel that extensive quilts has caused some distortion, you can smooth out your quilt on a flat surface such as the floor or a wall. You must be able to pin the edges of the quilt. Stretch the quilt slightly so that it is square and dampen with a spray bottle of water. Use a ruler or plumb lines to be sure the vertical and horizontal seam lines in the quilt are straight. Pin in place and allow quilt to dry overnight.
Later, after you have batted and quilted your piece, you will do this again so that the entire quilt is square before adding binding.
To measure for simple butted borders
Lay the quilt on a flat surface and measure through the middle from top to bottom. This gives you the side measurements. Cut two identical strips and sew on.
NEVER JUST SEW FROM ONE END TO THE OTHER WITHOUT PINS! Pin the middle of the strip to the middle of the quilt, pin the ends, then pin the remaining areas, easing in any fullness. After stitching, press strips away from quilt. It helps if you put the area with fullness against the feed dogs. So if the border strip has the fullness, sew with the body of the quilt on top. If the quilt seems to have fullness, put the body against the machine. The feed dogs will help ease this fullness.
Note: You do not even have to actually MEASURE. You can just lay your border strip on the quilt and cut to the size of the quilt body. Cut two identical strips. This only works for butted borders.
Lay the quilt on a flat surface. Measure through middle, including the two borders you have just added. This gives you the measurement for the top and bottom. Cut two identical strips and attach as above. Press away from quilt. This method gives you butted corners. (And yes, before you ask, you can do it the other way around and put the top and bottom on first and the sides on last.)
The finished product looks like this.
The second and third borders on this quilt have cornerstones. In the second border, they are pieced 9-patch blocks. In the third border, the cornerstones are plain squares of a contrasting color. They can also be squares which you fussy cut so that a special motif, like a flower, is centered in each square.
In this case, you would measure the center of the quilt in BOTH directions, without sewing on the first set of borders. Then cut the cornerstones to match the width of the strips. For example, if the striped border is 3 1/2" wide, the cornerstone would be 3 1/2" wide. Note that the striped border is actually three strips of fabric sewn together and treated as one fabric.
You would then sew on the two sides and press away from the quilt. Sew one cornerstone unit to each end of the remaining border strips. Attach these to the top and bottom of the quilt. Press.
Other Ways to Measure
Tip: Since I always square my units as I go and then square my blocks before assembling the quilt, I trust that a 12" block is really a 12" block and not 11.75" or 12.25". Therefore, I prefer using the method outlined below. Take note, however, that this only works on straight sets. If you have set your blocks on point, the measurement through the middle of the block is actually 1.414 X the outside measurement, a number I would just as soon NOT multiply out.
You may also choose to just count the number of squares in your quilt and multiply. If your quilt is 5 blocks across by 3 blocks tall and if the blocks are 12", the vertical measurement is 3 X 12" = 36" + 1/2" for seam allowance. The horizontal measurement is 5 X 12" = 60" + 1/2".
If you are making a butted seam, you must choose one of these measurements and add the width of the border. So, if you are adding 3" borders and want to add this to the short sides (because this will make the best use of the fabric width), you will have 36" + 3" + 3" + 1/2".
Did you get it? We have added 3" for EACH side border width plus our 1/2" seam allowance. You do not add the seam allowances from the seams that will be sewn between the cornerstones and the border strips.
If you choose to do cornerstones, you just count your blocks, multiply, then add cornerstones the width of your border strips in each corner.
Measuring for Miters
A mitered seam is measured in the same way but you must add another 2" on EACH side for the miter. In our example, the math would look like this:
2" + 3" + 36" + 3" + 2" + 1/2" seam allowance
(we are adding both seam allowances in one step by using 1/2")
If you think of it in small, one step pieces, it is not difficult at all. I actually draw myself a little sketch, adding each border, and then I can visually SEE that there need to be TWO sets of numbers added, one for each side.
Attaching borders to form mitered corners is a little bit different. You begin by sewing all four borders on the quilt. Each border piece is marked so that the amount you have left for the miter is not sewn to the body of the quilt.
In other words, in the example above, you would mark the border strip 5 1/4" from each end. The seam allowance belongs to the main quilt BUT actually is not sewn. When you sew, you will have the border width and miter amount (5") + the seam allowance from the quilt hanging loose at the ends.
Stitch to within 1/4" of the edge. Take a look at the corner.
The two borders are in different colors so you can clearly see that they come together at a right angle. To make this angle, you have to work on the right side (rotating the quilt so the corner you need is always to the upper right).
Take the side border and bring it to the top, matching the top edges and having right sides together. This should put a fold exactly in the middle of the quilt corner at a 45° angle. Using your long ruler, place the 45° angle across the top of the border, so you can draw a line along the edge of the ruler from the corner of the borders to the intersection with the quilt corner as shown in the diagram. Stitch from the quilt out to the edge, starting your stitch in the last stitch you used to attach the borders. Open and check that there is no gap in the stitching and the end pieces come out evenly. Press. Then (and only then!) trim away excess. Repeat this same procedure on all four corners.
By not trimming the excess fabric until you are satisfied, you are completely free to do this over. Once cut, it is almost impossible to make corrections.
If your quilt has more than one border, you can sew them together and treat them as one so that you only have to miter each corner once. There is an important trick to remember here. Each border will have the width of the last border added to its main measurement. (Twice, right? Once for each side.)
When you pin them together to sew, it is important that you begin by pinning from the middle. The ends of each border unit will look like stair steps, since each successive border piece will be larger than the one before it. Follow the rules above for attaching the first border and the others will naturally be in the right place. For practice, try this once on a 12" square - add multiple borders and practice your mitering skills without wasting a lot of fabric.
Figuring Out the Fabric Requirements for Borders
If you use fabric cut from the lengthwise grain of your fabric, you may end up with unpieced strips. You have to plan for this from the beginning. Using the lengthwise grain means that the fabric has no stretch or give.
When you cut border strips across the width of the fabric, you are still on the straight grain but you do get a small amount of give. These shorter pieces have to be pieced for long borders and this should be done using a diagonal seam. This makes the join almost invisible on print fabric and much less obvious on solid fabrics. This kind of seam uses more fabric than a butted seam.
Let's look at the anatomy of a 45º seam. The illustration shows the two pieces face to face with the top piece extending about 1/2" at the side and have the under strip sticking out 1/2" at the top. You can then sew in a straight line between the two intersections that are formed. Open and check that the strips meet evenly. When you are satisfied, you can trim to your normal seam allowance.
On each join you lose the width of the strip plus the amount you overlapped. The overlap can include the selvedge since it will be trimmed off.
Formula for Pieced Border Strips
Quilt is 70" x 45"
Borders are 2 1/2" wide finished
Fabric is 40" wide
original total length of border = 230"
230 ÷ 40 = 5.75 (round up to 6 which means 5 seams)
add width of strip plus 1" for each 45º seam
3+1 = 4" x 5 seams = 20"
add the amount needed to miter each corner (2" for each end of a border strip) + 1/4" seam allowance for each end = 4 1/2" needed to complete EACH miter
4 corners x 4.5" = 18"
add these two numbers to your original total
230 + 20 + 18 = 268 total pieced length needed for borders
divide again by the width of the fabric
268 ÷ 40 = 6.7 (round up to 7)
This is the actual number of strips you need to cut to make your pieced borders. You can sew them all together and treat the strip as one piece to cut the lengths needed
for each side
These numbers might change again if your reason for using pieced borders strips is artistic. For example, if you have made a landscape quilt and wish to have the border mirror the nearest color in the quilt, you would have to measure that area and cut a strip that was the right length.