How We Verify Our Calculators
A calculator is only as useful as the figures behind it. A wrong coverage rate or a misread paint spec sends you to the art shop with the wrong order, so we hold every number on this site to one rule: trace it to a real source, never guess. This page explains what that means in practice.
The process
- ✓Every rate and figure is traced to a named source category: manufacturer technical data (Winsor & Newton, Golden Artist Colors, Liquitex and others), and hand-worked test examples.Daler-Rowney, Schmincke, Speedball, Caligo), published standards such as ISO 216 paper sizes, Fine Art Trade Guild framing guidance, and UK supplier and carrier data (Jackson’s Art, Royal Mail).
- ✓Every calculator is tested against hand-worked examples with expected answers derived independently of the code, so the maths is checked as well as the source figure.
- ✓Figures are adversarially re-checked: an auditor re-derives each result from the source from scratch and compares it to the calculator’s output, rather than assuming the existing number is right.
- ✓Where coverage or shrinkage varies by brand and technique, we say which figure the calculator uses and why, and let you enter your own rate instead.
- ✓Errors reported through the feedback buttons are investigated against the original source, fixed, and re-verified before the fix goes live.
- ✓Content is reviewed when sources change, such as updated manufacturer datasheets or revised Royal Mail pricing, and each calculator carries a last-updated date.
Verified, not guaranteed
These calculators give working estimates, not guarantees. Paint coverage, drying times and material quantities vary with brand, pigment, surface and technique, so confirm quantities with your supplier before a large order. For framing or hanging valuable or heavy artwork, consult a professional framer or conservator, and check pricing, shipping and insurance figures with your carrier or insurer before relying on them.
Spotted an error?
Every calculator page has feedback buttons. If a figure looks wrong, tell us what you entered and what you expected: we investigate against the original source, fix anything that fails the check, and re-verify before the correction goes live. When a report shows a genuine error, the fix lands on the affected page itself, with a dated correction note where it matters.