The six sizes that get confused
| Term | What it means | What it cannot establish alone |
|---|---|---|
| Visible glass | The exposed glass you can see between glazing stops or sash components. | Overall window frame size, glass edge size or emergency escape opening. |
| Finish opening | A dimension between named interior or exterior finish surfaces: drywall, casing, brick or trim. | The concealed frame or rough-opening boundary. |
| Retained-frame opening | The clear space left inside the frame members that the scope keeps. | The clearance, sill profile or dimensions of the new insert. |
| Rough opening | The building opening prepared to accept the assembly, usually bounded by framing or a defined masonry/buck detail. | The factory’s net frame dimension. |
| Frame / unit size | The product dimension identified on its drawing. Confirm whether fins, flanges, brickmould, receptors or other projections are included. | The full assembly’s installation path or finish coverage. |
| Order-entry size | The particular size basis accepted in the supplier’s system. | Whether the factory applies a deduction unless that mode is explicitly documented. |
Name the parts before taking dimensions
The head jamb is the top frame member; side jambs are the vertical members; the sill is the bottom frame member. A sash carries the glass. Stops, jamb liners, tracks and weatherstripping can project into the space you are measuring.
The interior stool is the shelf-like finish at the bottom of many wood windows. Its top is not automatically the true sill reference. Casing covers the interior joint. Brickmould is an exterior trim profile; its name does not prove the wall is brick.
A buck is a framed or specified mounting surround within a masonry opening. A receptor is a receiving frame or channel designed to accept a window. A mull joins adjacent units. Each may reduce available space or change the assembly dimensions.
Keep trade language, but define the scope
“Wood-out,” “metal-out,” “jump frame,” “retrofit,” “pocket” and “full-frame” may carry different meanings between regions, dealers and manufacturers. Put the trade term on the record, then explain it in plain words.
For example: “Wood-out category; remove both sashes and jamb liners; retain original side jambs, head and sill; install a block-frame insert.” Another job may use the same trade label for a different removal boundary. The written boundary governs the measuring plan.
A familiar 32W × 54H family is a recognition aid. Measure each opening independently, including openings that look identical. Size codes can describe nominal families rather than actual inches.
Use one recording convention
Write width × height, label the units, and keep fractions explicit: 32 1/16 in. Use separate fields for width and height so a note cannot silently reverse them. Record the observed reading before making a conversion required by the selected product.
If working in millimeters, keep the original millimeter reading. One inch equals exactly 25.4 mm, but conversion does not improve an uncertain observation. Do not switch between rounded inch and metric values several times on the way to an order.
Source notes
Manufacturer requirements apply only to the named products and applications. The field procedures and worked examples here are an educational synthesis.
- JELD-WEN · Wood/clad pocket measurement guide JMI001 ↗
Pocket and net-frame ordering modes, measuring surfaces, geometry checks and product-specific limitations.
- Marvin · Narrow frame and insert measuring instructions 19970684 ↗
Inside-opening versus frame-size ordering and sill-angle geometry. Dated May 21, 2020; verify current applicability with the supplier.
- Pella · Full-frame replacement without disturbing brick or siding, FF_BFBS ↗
Block-frame details addressing exterior openings, drywall returns, depth, blocking and flashing. Revision March 31, 2023.