Read feet, inches and fractions
A single prime or apostrophe conventionally indicates feet; a double prime or quotation mark indicates inches. Write explicit units when a copied value could lose those marks. Read a mixed fraction as a whole number plus a fraction: 2 1/2 inches is 2.5 inches.
Convert feet to inches first, add the remaining inches, then multiply by 25.4 for millimeters. NIST defines one inch as exactly 25.4 mm. The conversion is exact; the precision of a field measurement is a separate question.
| Feet and inches | Total inches | Millimeters |
|---|---|---|
| 3 ft 0 in | 36 | 914.4 |
| 4 ft 0 in | 48 | 1219.2 |
| 6 ft 2 1/2 in | 74.5 | 1892.3 |
| 8 ft 0 in | 96 | 2438.4 |
For the third row: (6 x 12 + 2 + 1/2) x 25.4 = 1892.3. Do not read 6 ft 2 1/2 in as 6.25 feet. If the unit or fraction is illegible, retain the source text and flag it for clarification.
Separate codes from measured sizes
A manufacturer code identifies a size within that manufacturer's convention. It is not automatically an exact frame measurement. Do not convert a four-digit code into millimeters without checking its chart and the associated dimension labels.
Keep width and height in separate fields, with units and size basis. Preserve the order stated in the source. A number may refer to a rough opening, frame or another measurement; identify the dimension basis before applying it to a model or brief.
For product-specific dimensions, start with the manufacturer's current sizing documents, such as Andersen's sizing resource directory. This guide provides arithmetic examples, not a standard-size catalogue.
Compare display rounding with exact values
Fenestry stores house geometry in millimeters. Its feet-and-inches display rounds to the nearest 1/16 inch. Switching display units does not replace the saved geometry with the rounded display value. The approximation indicator warns when the displayed value differs from the stored dimension.
| Saved value | Feet-and-inches display | Interpretation |
|---|---|---|
| 1892.3 mm | 6 ft 2 1/2 in | Exactly representable at the display increment |
| 1829 mm | Approximately 6 ft 0 in | 1828.8 mm is the exact conversion of 6 ft |
To inspect the behavior, open the editable example and select F01, a fixed glazing opening, in Windows and doors. Enter 6 ft 2 1/2 in in its width field and leave the field to apply the change. Check that no rejection is shown, switch to millimeters to inspect 1892.3, then export the schedule and compare F01's numeric width. Product checks may reject a different opening or dimension. Confirm that the model accepted an edit before using the export as evidence. This is a deliberate model edit, not verification of a real building.
Check exported numbers alongside their column headings. A rounded label on screen should not become a new source measurement merely because it is easier to read.
Record units explicitly
Keep the original notation, normalized numeric value, units, size basis and source reference together. An omitted unit should remain a question until the drawing context or responsible person resolves it. Do not silently assume that every sheet in a combined PDF uses the same convention.
The blank schedule and field dictionary provide a place for those distinctions. Use the takeoff review workflow to check imported dimensions against their original sources before supplier discussion.