Editorial Policy

Last updated: 19 April 2026

FibreCalcs publishes free calculators and educational content for sewing, quilting, knitting, and crochet. Every result depends on the accuracy of the underlying formula, and every piece of educational content shapes how people plan their projects. This page explains how formulas are sourced, verified, and tested, how content is reviewed, and how errors get corrected.

Formula sourcing

Every calculator on FibreCalcs implements a formula drawn from a published reference. I don’t invent the mathematics. The standard formulas used by professional curtain makers, quilters, and knitters are well-established; my job is to implement them correctly, present them clearly, and cite the source so readers can verify the work themselves.

Sources differ by pillar. Below is what I reach for in each area.

• Sewing and curtain making.Singer Sewing Reference Library, Simplicity and McCall’s published pattern yardage charts, and professional workroom practices documented by Cindy Taylor at sew-helpful.com. Fabric weight classifications follow ASTM International textile standards.
• Quilting.Missouri Star Quilt Co educational resources for piecing and finishing techniques, Robert Kaufman Fabrics’ published fabric width specifications (42-inch usable width is the calculation default for quilting cotton), and standard bed dimensions drawn from mattress industry sizing data. Pre-cut dimensions (charm packs, jelly rolls, layer cakes, fat quarters) are verified against multiple manufacturer specifications.
• Knitting and crochet.The Craft Yarn Council’s Standard Yarn Weight System for weight classification and gauge expectations, manufacturer-published yards-per-weight data for specific yarn put-ups, and gauge standards documented in pattern publications.

Each calculator page cites its specific source in a dedicated reference block. Where multiple sources agree on a formula, I cite the most accessible one. Where sources disagree, the page notes the discrepancy and explains which approach FibreCalcs uses and why.

Formula verification and testing

Citing a source isn’t enough. Every formula goes through a four-step verification before it appears on the site and then stays under automated test coverage for the life of the page.

1. The formula is implemented in code and checked against known input and output values from the cited source.
2. At least two worked examples are run through the calculator. Every intermediate value and final result in the prose matches what the code produces.
3. Automated tests are written for the primary scenario and at least one variant or edge case. If a later code change breaks the formula, the tests fail and the change is blocked.
4. Source links are checked to confirm the referenced material is still accessible and the cited information still matches the formula in use.

The test suite currently runs 188 automated tests across 28 test files. It runs locally before every push and again in continuous integration on every pull request. Nothing ships to production with a failing test.

On top of automated testing, a subset of calculators has been reviewed by qualified professionals whose field matches the calculator’s subject. The current reviewers are mathematics academics who verify the formula and its implementation. The programme is expanding to textile-domain reviewers — quilting instructors, professional curtain makers, and knitwear designers — who will check the craft assumptions that sit on top of the maths. Pages that have been reviewed display the reviewer’s name and affiliation below the title.

Worked example validation

Worked examples on every calculator page use inputs that are actually run through the calculator function. The intermediate values — pattern-repeat-adjusted drop length, seam allowance totals, purchase rounding — are captured from the function output, not hand-typed numbers that approximate what the calculator would say. If the formula changes, the test suite fails, the example is updated, and the review date is incremented.

Each worked example has four parts: a real-world scenario, a step-by-step calculation with intermediate values, an interpretation of what the result means in practice, and a takeaway with actionable advice. You can see the pattern on the curtain fabric calculator, the quilt backing calculator, and worked through in full in the curtain fabric guide.

Content review cycle

Fabric specifications and industry conventions change over time. Quilting cotton widths, yarn put-ups, and recommended seam allowances all drift slowly. To keep content accurate, three dates are tracked on every page.

• Last updated— the date the content was last meaningfully revised. Shown to readers and emitted in the page’s structured data for search engines.
• Content review date— an internal date tracking when the page was last reviewed for accuracy, even if no edits were made. Used to queue pages for re-verification.
• Cost data expiry— for any calculator that references material costs, the date after which those costs should be re-verified. Set at six months from the last verification.

These dates aren’t cosmetic. Every content file in the codebase carries the fields, schema validation checks they’re present, and pages approaching their review date are queued for re-verification rather than left to drift.

AI disclosure

FibreCalcs is built with the assistance of AI tools for code generation, content drafting, and test scaffolding. I’m transparent about this because it matters for trust. Here is what AI does and doesn’t do on this site.

• AI does not decide which formulas to use or how to present results. Those are editorial decisions made by a human.
• Every formula is human-verified against published textile industry sources before publication.
• Every worked example is validated by running the actual calculator code, not by asking an AI to produce plausible- looking numbers.
• Content is scanned by an automated validator for AI-typical patterns (vague language, generic phrasing, banned heading formats). Flagged content is rewritten before it ships.

AI helps me build faster. Industry sources and automated testing are what make sure I build correctly. More on who’s behind that verification is on the about page.

Source citation and accessibility

Every calculator page includes two types of source information.

• A formula source field naming the specific reference (book, article, or standard) from which the calculation method is drawn.
• Source links providing direct URLs to supporting references, where available, so readers can verify the maths independently.

Every link is checked before publication. If a cited source goes behind a paywall or becomes unavailable, the citation is updated to a publicly accessible alternative. I never fabricate citations — if a verifiable source can’t be found for a particular method, the page says so rather than inventing a reference.

Error reporting and corrections

If you find an error in any calculator, worked example, or educational content, use the feedback form on any page to report it. Include the specific calculator, the inputs you used, and the result you believe is incorrect.

Every report is reviewed. When a report is confirmed as a real error, the correction process is:

1. Verify the issue by running the reported inputs through the calculator and against the cited source.
2. Fix the calculation in the code.
3. Update the affected worked examples so their numbers match the corrected function output.
4. Run the full test suite to confirm no other calculator depends on the previous incorrect behaviour.
5. Increment the page’s last-updated date and reset the content review date.

Calculator accuracy matters. A wrong result means someone buys too little fabric, runs out of yarn mid-project, or cuts a set of curtains short. I’d rather hear about errors than let them persist.

Independence

FibreCalcs is independently operated. There are no affiliate relationships with fabric shops, yarn suppliers, or pattern companies, and results aren’t influenced by any commercial interest. When a brand is mentioned in educational content, it’s for context only — not because of compensation. The site is free, carries no advertising, and requires no login.