Sashing & Border Width
Inner and outer border maths for block quilts.
Finished strip between blocks.
Finished outer frame.
Usable width of your strip fabric.
76 x 76 in
Finished top with sashing and border, cut strips about 2 yd.
- Sashing strip width
- 2.5 in
- Cross strips
- 20 x 12.5 in
- Lengthwise strips
- 4 x 68.5 in
- Border strip width
- 4.5 in
- Side borders
- 2 x 68.5 in
- Top and bottom borders
- 2 x 76.5 in
All cut sizes already include a quarter-inch seam allowance on each edge. Cut the short cross strips first against the blocks, then run the long lengthwise strips past the joins, and add the side borders before the top and bottom so the corners mitre cleanly.
About This Tool
The Sashing and Border Width calculator turns a stack of finished blocks into a real quilt top, working out the grown dimensions and the exact cut strips you need for the sashing between blocks and the frame around the edge.
You enter the block count, the finished block size and your chosen strip widths.
It returns the finished top plus every cut strip length and count, seams included.
The answer ends the running short of a border strip halfway through a layout.
Sashing and border quietly enlarge a quilt far more than a plain block count suggests.
Cutting the strips to a plan beats slicing them off a roll by eye.
One tidy layout sheet lets you piece the whole frame with every block already accounted for.
Why Sashing & Border Width Math Matters
Sashing adds a strip to every gap, so a quilt grows wider than blocks alone predict.
Borders frame all four sides, and forgetting one leaves a top that will not square to a bed.
Cut strip lengths must include seam allowance or every join comes up a quarter inch short.
The lengthwise sashing runs past the cross strips, so its cut length is not just one block.
Side borders are added before top and bottom, or the corners will not mitre cleanly.
Counting strips up front stops a half-finished frame staring at you from the design wall.
Knowing sashing yardage lets you buy a matching or contrasting strip fabric deliberately.
A planned frame turns a ragged block pile into a quilt that reads as designed.
The Formula
The finished center is the blocks plus the sashing in every gap, the borders add two more widths to each direction, and each cut strip is its finished size grown by twice the seam allowance, with the strip areas summed into a yardage.
- Center size —
- the blocks plus the sashing between them, before any outer border
- Cut strip —
- a finished strip width or length grown by a seam allowance on each edge
- Strip yardage —
- the total strip area divided by the bolt width to give the length to buy
Because a cross strip only spans one block while a lengthwise strip spans the whole row, the two are cut to different lengths even though they share one finished width.
Worked Example: Step by Step
- 1You lay out a five by five grid of finished twelve inch blocks.
- 2You choose a two inch sashing and a four inch outer border.
- 3The center measures five twelve plus four twos, giving sixty eight inches.
- 4Adding borders on both ends brings the finished top to seventy six square.
- 5Each cross strip is cut two and a half wide by twelve and a half long.
- 6There are twenty of them, since four gaps run through each of five rows.
- 7The four lengthwise strips each span the grown center width past those cross joins.
- 8The tool totals the strips and borders at roughly a yard and a quarter of fabric, rounded up so a join is never cut short.
How to Use This Calculator
- Set the number of blocks across and down the grid.
- Enter the finished block size, not the cut size.
- Type your sashing and border finished widths.
- Set the usable width of your strip fabric.
- Read the cut strip sizes and how many to cut.
- Add the side borders before cutting the top and bottom ones.
Key Terms
- Sashing
- the strips of fabric set between blocks to separate and frame each one
- Border
- the outer frame of fabric added around the whole quilt top
- Cross strip
- a short sashing strip set between two blocks within a single row
- Lengthwise strip
- a long sashing strip that runs past a whole row of blocks
- Mitre
- a diagonal corner join that lets two border strips meet cleanly
- Seam allowance
- the extra width beyond a finished size that a stitched seam consumes
- Design wall
- a vertical surface where blocks and strips are laid out before being sewn
Sashing & Border Width Reference Table
| Strip type | Cut length rule | Cut count |
|---|---|---|
| Cross sashing | block + 2 SA | gaps times rows |
| Length sashing | center width + 2 SA | rows minus one |
| Side border | center length + 2 SA | two pieces |
The lengthwise strips and the top and bottom borders are always the longest cuts because they run past the joins rather than stopping at them, so measure and cut those last after the shorter cross strips and side borders have fixed the size they must span.
Common Mistakes & Pro Tips
- Cutting every sashing strip to one block length so the long runs fall short at the joins.
- Forgetting seam allowance on strip lengths and ending each join a quarter inch light.
- Adding top and bottom borders first, then finding the corners cannot mitre over the side borders.
- Sizing the finished top from blocks alone and being shocked when sashing adds a foot.
- Buying one strip fabric for a bold border without enough for a matching repeat.
- Counting sashing gaps as one fewer than they truly are down each outer edge.
Real-World Use Cases
- Framing a sampler quilt with a single sashing.
- Planning strip cuts for a five by five block grid.
- Choosing an outer border to reach a bed size.
- Budgeting contrast fabric for sashing and borders.
- Teaching the cross-versus-lengthwise strip difference.
- Adding a sashed frame to a charity quilt of donated blocks.
- Turning finished blocks into a bordered top layout.
Sashing & Border Width: Frequently Asked Questions
Why are the lengthwise strips longer?
A lengthwise strip runs past an entire row, including the cross strips you set first, so it spans the full center width rather than a single block. Cutting them to block length leaves every horizontal run a panel short.
Do the cut sizes already include seams?
Yes, every strip length and width shown already grows the finished measurement by a seam allowance on each edge. That means you can cut straight to the numbers without adding a quarter inch by hand.
Which borders go on first?
Add the two side borders before the top and bottom ones, so the long horizontal strips span the grown width and the corners mitre cleanly. Reversing the order forces a border to stop short of a corner.
How much sashing fabric should I buy?
The tool totals every strip area and turns it into a yardage at your bolt width, so buy to that figure rounded up. Add a little more if the strip fabric is directional and must be matched across joins.
Can I skip the sashing entirely?
Yes, set the sashing width to zero and the top becomes a plain grid of blocks with borders only. Sashing is optional, but it frames busy blocks and gives a quilt extra size without adding whole blocks.
This page explains how the sashing & border width works, what each input means and where the numbers come from, so you can plan your next make with confidence.
Written by Bobbin & Form Editorial Team
Home sewists & machine-embroidery practitioners
Reviewed by Marie Delacroix
Custom sewist & machine-embroidery technician, 15 years at the machine
Formulas follow standard sewing and needlework references. Results are estimates — always confirm against your pattern and a pre-washed swatch.
Sources & further reading
- Threads Magazine — fabric cutting & yardage guides
- ISO 13934 — textile tensile & fabric property standards
- Your local fabric store's bolt-width charts