How We Verify Our Conversion Factors

To verify a conversion, identify the quantity and unit convention, read the applicable primary definition, calculate independently, then compare displays at the same rounding. This walkthrough uses a hypothetical 2-inch length. The methodology page describes the site’s implemented calculation and publication checks.

1. Identify the quantity and convention

The example measures length using the international inch. It does not describe an area or a nominal product size. NIST’s revised unit table gives the international foot as exactly 0.3048 m. NIST Handbook 44 Appendix C gives 12 inches per foot. Therefore:

1 international inch = 0.3048 m / 12 = 0.0254 m
2 inches × 0.0254 m/inch = 0.0508 m = 5.08 cm

The length workflow explains measured dimensions. For a squared quantity, use the area workflow and square the linear factor. For example, 1 square international foot is (0.3048 m)² = 0.09290304 m². Do not apply a length factor once to an area amount.

2. Read the definition behind the displayed factor

A source must support the specific claim. BIPM’s SI definitions and decimal prefixes explain SI units and their decimal multiples. NIST Appendix B.8 contains both exact and approximate values. Its table is not uniformly exact.

For mass, NIST footnote 22 states the exact avoirdupois pound of 0.45359237 kg. The reciprocal kilogram-to-pound ratio is 1 / 0.45359237; a decimal such as 2.20462262 is rounded. The mass workflow distinguishes avoirdupois, ton and metric carat conventions.

For data, NIST’s binary-prefix reference distinguishes 1 MB = 1000000 bytes from 1 MiB = 1048576 bytes. Use the data workflow to choose the named prefix before comparing a result.

3. Choose the appropriate calculation

Linear units use a common base unit. Temperature needs offsets: NIST’s temperature formulas give (68 °F − 32) × 5/9 = 20 °C. A temperature interval needs different treatment from an absolute reading.

The fuel workflow distinguishes proportional economy-to-economy conversions from reciprocal consumption-to-economy conversions. For a hypothetical 30 US MPG, the calculation is:

100 × 3.785411784 L/US gallon ÷ 1.609344 km/international mile
= 235.214583333…
235.214583333… / 30 ≈ 7.840486111 L/100km

The full US gallon is derived from 231 cubic inches in NIST Handbook 44 Appendix C, together with the international inch. US and Imperial gallons must be named explicitly. Converting a stated fuel value does not establish a vehicle rating or a driving outcome.

4. Check cross-quantity assumptions

The cooking tools use original ingredient portions from King Arthur’s own chart: for example, 120 g per author cup of all-purpose flour. Half of that portion gives an estimate of 60 g. Scaling uses the stated assumption 1 cup = 16 tablespoons = 48 teaspoons. The source does not specify its cup volume in mL; the portion is not a verified physical density.

A mL-to-mass result requires independently verified density. NISTIR 7383 (2019), GLP 10 Table 2 gives 0.99820675 g/mL for air-free water at 20 °C. Under that condition, 100 mL × 0.99820675 g/mL = 99.820675 g before display rounding. This density is a condition-specific reference, not an exact universal constant. Rice currently has no verified portion or density in the ingredient model, so cross-quantity results are unavailable.

The unit-system reference identifies physical unit conventions. Clothing charts are static correspondences with their own stated scope; a source label alone does not demonstrate a completed manufacturer audit.

5. Compare equivalent display precision

The underlying calculations use stored JavaScript numbers and floating-point arithmetic. The unit widget defaults to four decimal places, while category pillar references display ten significant digits. Pair conversion tables and ingredient results have other rounding policies, documented on the methodology page. A pair’s authored formula or example is separate from the canonical factors; its displayed digits are not guaranteed to expose full internal precision.

For the 2-inch example, both 0.0508 m and 5.08 cm describe the same calculated length. Extra digits do not improve the original measurement’s accuracy. Compare results at the same rounding, using the full applicable definition or source value before rounding the final answer.

6. Interpret checks and review dates

A published pair’s “Last reviewed” date must match its explicit publication record. Automated checks validate required fields, unit names, date rules and HTTPS source syntax, and compare finite authored examples with production calculations using a 0.1% relative tolerance for nonzero results. The checks do not open external sources or verify every statement in an explanation or FAQ. Passing them does not independently establish the truth of a source claim.

This walkthrough was reviewed October 6, 2026. Dates record actual content reviews; they are not a promise of scheduled re-review or evidence of a universal source audit. If you find a discrepancy, use the contact page with the URL, input, named unit convention, expected arithmetic and primary evidence.