Quilt Backing CalculatorAbout Quilt Backing Calculator
Quilt Backing Calculator is a small, free toolbox for the fabric arithmetic of quilting — backing, batting, binding, borders, sashing, blocks, sizes and half-square triangles — built and maintained by one person.
Why I built it
The backing is where a quilt goes wrong at the very last step. A top can sit finished for months — pieced, pressed, done — and then stall completely, because the back is not just one big piece of fabric. It has to be pieced from widths that don't match the quilt, the panels can run two different ways, every seam eats its allowance, and the whole thing still has to finish bigger than the top on every side. Get any part of that wrong and you come up short — six inches short is the classic — with the quilt all but layered in your head and the shop possibly sold out of your fabric.
So the backing calculator on the homepage doesn't hand you a single number. It costs your backing both ways — panels running lengthwise and panels running crosswise — and shows the yardage, the panel count and the leftover for each, so the cheaper orientation is a fact rather than a hunch. And where a quilt is wider than one fabric width can handle gracefully, the diagonal method from John Flynn's published lesson is here too, with his own worked numbers reproduced on the page so you can check the tool against its source. Every tool on this site follows the same rule: show the working, name the source, and let you argue with the arithmetic before any fabric is cut.
About the author
I'm Ian Welkins, an independent web developer based in Houston, Texas. I build small, single-purpose calculator websites for jobs where a wrong number costs real material — tools that do one job, show their working, and ask for nothing: no sign-up, no accounts, nothing to install.
This site is researched, built and maintained by me personally. The methods behind the calculators follow the published sources named on each page — Flynn's diagonal lesson, The Warm Company's batting sizes, the commonly published size charts — and every formula is tested against hand-worked examples before it goes live; the worked examples you see on the pages are generated by the same code that runs the tools themselves. When a reader reports a number that looks off, I check it myself.
You can find me, and check that for yourself, on these profiles:
- GitHub — my projects and code
- Dev.to — notes on building these tools
- About.me — all my sites and profiles in one place
- Gravatar — my verified profile
If a yardage figure on this site ever looks wrong, tell me through the report-an-error page — I read every report myself and fix what's wrong. For anything else, the contact page is the way to reach me.
A note on AI
I use AI tools to help draft the text and code on this site, the way many independent developers do now. The numbers are a different matter: every yardage figure comes from the methods and published sources named on the pages, worked through the calculators' own arithmetic, and I verify the results against hand-worked examples before anything is published. If a number is wrong anyway, the error report doesn't disappear into a system — it reaches me, a person, and I fix it.
How the numbers are sourced
Most formulas on this site follow published quilting methods, and each calculator page names the source it follows: John Flynn's diagonal backing formula, Missouri Star Quilt Co.'s perimeter-plus-allowance binding method, The Warm Company's standard pre-cut batting package sizes, and the commonly published quilt and mattress size charts. The diagonal backing calculator implements Flynn's formula exactly, worked example included, and the page reproduces his own numbers so you can verify it. A few tools, though, rest on modeling choices of this site's own rather than a published formula — the per-panel usable-width model behind the backing calculators, and the way the sashing and border tools pack strips across a fabric width. Where a calculator makes a modeling choice like that, the page states the choice plainly and tells you how to adapt the result.
Every worked example on the site is generated by the same code that runs the calculators, and that generated output is verified in QA against hand-computed cases. When a quilter reports a discrepancy, it is investigated and, if the site is wrong, corrected publicly — the editorial policy describes how, and the error report form is always open.
What the site is not
It is not a shop: nothing is sold here, and no calculator result is influenced by anyone's fabric inventory. It is not a pattern library or a tutorial channel — it does one job, the arithmetic, and links you onward for the rest. And it is not finished: quilting has more fabric questions than any one site launch covers, and the toolbox grows as readers ask. Start with the backing calculator — it is the tool the site is named for, and still the one most quilters need first.