Measure the unobstructed space through the normally opened window, not the frame or glass. Record clear width and height separately, then calculate their rectangular area in square feet. Keep floor height, operation and exterior access as separate checks. A worksheet can organize observations; it cannot approve an installation or verify the measurements entered.
Which dimensions should stay separate?
Use three labels on your notes: wall opening, window unit, and clear opening. They answer different questions. The contractor needs the wall opening to plan the installation, the supplier needs the unit configuration, and the escape assessment needs the usable opening. Do not transfer a number from one column into another just because it is the only dimension available.
Manufacturer documentation makes the distinction visible. Andersen’s A-Series casement tables list clear opening separately from glass and overall unit area. The corresponding document for your exact product is a better starting point than assuming every window with a similar outside size opens equally. Andersen opening data.
What should the initial measurement sheet contain?
| Field | Record | Important boundary |
|---|---|---|
| Address and jurisdiction | Property address and actual municipality | Postal city alone may not identify the building authority |
| Proposed use | Bedroom, other room, existing-window replacement | Use the same description throughout the project |
| Manufacturer/model | Label and hardware configuration if known | Unknown is better than a guessed model |
| Clear width | Narrowest usable width in the normal open position | Do not use outside frame width |
| Clear height | Usable height in that same position | Do not add space available only after dismantling parts |
| Floor relationship | Finished floor and bottom of usable opening | Have the installer confirm the applicable measurement method |
| Outside arrangement | Well, cover, ladder/steps, deck or other obstruction | Area arithmetic cannot assess the route outside |
| Evidence | Photos and product sheet | Initial homeowner measurements are not order dimensions |
Do not force damaged hardware, remove parts or enter an unsafe well to complete the sheet. Leave a field unresolved and have the contractor inspect it. There is no benefit in making an uncertain number look precise.
How do you calculate rectangular opening area?
Multiply width by height in the same units. When both inputs are inches, divide by 144 to convert square inches to square feet. Keep the unrounded result for comparisons; rounding a displayed result should not turn a value below a threshold into one above it.
| Hypothetical measured opening | Calculation | Area, rounded for display |
|---|---|---|
| 20 × 24 inches | 480 ÷ 144 | 3.33 square feet |
| 24 × 30 inches | 720 ÷ 144 | 5.00 square feet |
| 30 × 28 inches | 840 ÷ 144 | 5.83 square feet |
| 18 × 48 inches | 864 ÷ 144 | 6.00 square feet |
The fourth example is useful: a tall, narrow rectangle can have more area than a shorter, wider one. That does not answer whether its width is acceptable. Likewise, an opening can satisfy two individual dimension checks without supplying enough area. The main planning guide presents a sourced KCMO reference table; check the applicable criteria with your authority.
These four examples are original calculations, not measurements of products or completed projects. They are not a list of compliant window sizes.
What if the opening is irregular or the hardware occupies space?
Use the manufacturer’s documented clear-opening method and have the installer resolve what counts. Do not convert a difficult-to-measure shape into an ideal rectangle simply to make the calculation easier. Record the obstruction and provide a photograph or drawing with the question.
Also identify the operating hardware. A specification sheet for a related model or a different hardware option may not describe the unit being quoted. Keep the exact product identifier with the calculated result so the number is traceable.
How should you use the worksheet with an installer?
Send the observations as preliminary information. Ask the installer to confirm the dimensions, proposed model, applicable opening classification and any remaining checks. If the proposed replacement changes operation, ask for a before-and-after comparison using the same measurement labels.
Keep the final verified product data with the quote, and record any substitutions before ordering. A substitution is worth reviewing even when the outside dimensions appear unchanged, because the intended comparison is about the complete configuration.
For the full project, read the Kansas City egress-window guide. Then choose replacement, enlargement or new installation to prepare the right scope.