Changing a column heading from inches to centimetres does not change the measurements beneath it. Keep the source quantity and its unit together, then create a separate converted result so the transformation remains visible to the next reader.

Start with a small sample containing a known value. For a length table, put 12 in A2 and label that column Inches. Reserve another column for Centimetres. Do not mix rows with different source units under one unexplained heading.

Numbers CONVERT uses the form CONVERT(number, from-unit, to-unit). Apple’s unit codes are case-sensitive. For the sample, enter =CONVERT(A2,"in","cm") in the result cell. The documented metre unit accepts the centi prefix, giving cm; in is the inch code. Use the codes in Apple’s table rather than inventing abbreviations.

Verify the numerical transformation

Twelve inches should become 30.48 centimetres: 12 multiplied by 2.54. Check the result against that independent arithmetic and retain the original 12 beside it. A display rounded to 30.5 may be acceptable for one purpose, but it should not obscure what precision the report requires.

Use a second example appropriate to the real range of measurements before filling the formula across the entire table. Inspect the first and last converted rows and any negative or zero value that is meaningful for the task.

Temperature illustrates why a universal multiplication rule is unsafe. Apple documents C for Celsius and F for Fahrenheit. In a separate practice cell, =CONVERT(0,"C","F") should return 32, while =CONVERT(20,"C","F") should return 68. A temperature-scale conversion includes an offset as well as a scale factor.

Preserve the measurement meaning

If a conversion fails, verify the source type, exact codes and intended unit category. Do not turn an unexplained error into zero or silently choose a similarly named unit. Several measurement systems use familiar names for different quantities, so the source record must establish which one was intended.

Keep the conversion formula, source-unit label and result-unit label in the handover. Decide the output precision with the recipient and check the issued table for those units. The final values should be traceable back to the original measurements, not merely look plausible under a newly edited heading.

Reference: Apple: CONVERT function and supported units.