| Shape | Inputs | Quantity | Waste % | Notes |
|---|---|---|---|---|
| Rectangle / Sash | Width 1200 mm, Height 1500 mm, Frame 50 mm | 4 | 5 | Common double-hung opening, net glazing deducted. |
| Segmental Arch | Width 900 mm, Spring 1100 mm, Rise 220 mm, Frame 45 mm | 2 | 7.5 | Traditional arched head above rectangular body. |
| Semi-circular | Diameter 800 mm, Frame 40 mm | 1 | 3 | Fanlight or round-top transom profile. |
- Unit conversion: entered dimensions are converted to meters, then area is calculated in m².
- Rectangle: A = width × height.
- Ellipse: A = π × (width ÷ 2) × (height ÷ 2).
- Circle: A = π × (diameter ÷ 2)².
- Semi-circle: A = 0.5 × π × (diameter ÷ 2)².
- Segmental arch: A = (width × spring height) + segment area.
- Segment area: R = width² ÷ (8 × rise) + rise ÷ 2, then A = R²·acos((R − rise) ÷ R) − (R − rise)·sqrt(2R·rise − rise²).
- Frame deduction: net glazing uses (dimension − 2×frame) where applicable; arch rise is reduced by frame approximately.
- Waste factor: adjusted total = net total × (1 + waste% ÷ 100).
- Select the shape that matches the window opening.
- Choose your unit and enter measured dimensions.
- Enter frame width if you want net glazing area.
- Add quantity to total identical windows together.
- Set a waste factor when ordering glass or panels.
- Press Calculate Area to see results above the form.
- Use the CSV or PDF buttons for saved rows.
Surveying heritage openings with repeatable measurements
Heritage windows rarely sit perfectly square, so capture repeatable numbers. Measure width at head, mid, and sill, then record the smallest value for ordering. Do the same for height at left, center, and right. Enter those outer opening dimensions here, then apply an optional frame width to estimate clear glazing. This approach aligns site notes, drawings, and supplier checks without hiding irregularities. Photograph each opening and note any taper today.
Keeping unit conversions consistent across drawings and quotes
Restoration packages often mix millimeters, inches, and feet. The unit selector converts every entry to meters before area is calculated, then reports square meters with a square‑feet reference. Using one internal unit prevents rounding drift when you compare multiple windows, elevations, and option sets. For tender schedules, keep the same unit choice for an entire survey day and export results for auditability. Store exported rows with date and room labels.
Selecting the correct heritage shape for reliable takeoffs
Choose Rectangle for typical sashes and casements, Ellipse for oval lights, and Circle or Semi‑circle for roundels and fanlights. For curved heads above a straight springline, select Segmental Arch. The calculator models this as a rectangle up to the springline plus a circular segment defined by span and rise. That geometry matches many Victorian, Edwardian, and colonial profiles.
Frame deduction as a net glazing estimate and scope control
Frame width is treated as a uniform border that reduces the clear pane area. For rectangles and ellipses, net dimensions become width minus two frames and height minus two frames. For circular types, diameter is reduced by two frames. For segmental arches, width and spring height reduce similarly, and rise is reduced approximately to reflect top margins. If net dimensions reach zero, net area is set to zero.
Quantity totals, waste factor, and procurement confidence checks
Once a per‑window area is computed, totals multiply by quantity for budgeting and scheduling. Waste factor increases the net total by a percentage to cover cutting loss, breakage, and on‑site trimming, which is common with heritage glass, laminated panes, or protective panels. Compare gross versus net totals to confirm scope: opening repairs use gross, while glazing orders and coatings typically follow net plus waste.
FAQs
1) Should I use gross area or net glazing for estimates?
Use gross area for opening or masonry work. Use net glazing when pricing glass, acrylic, or secondary glazing. If you are unsure, export both and confirm with your supplier’s measurement rules.
2) What is the best way to measure an old window that is out of square?
Measure three points across width and height. Use the smallest measurements for ordering to avoid tight fits. Record the largest values separately for repair and reveal work calculations.
3) How do I choose values for a segmental arch?
Measure the springline width at the points where the curve begins. Measure spring height to that line, then measure rise from the springline to the highest point of the arch.
4) Why is waste factor limited to 50%?
Very high waste percentages usually indicate missing measurements or a different material takeoff method. A 50% cap prevents accidental over‑ordering while still allowing generous allowances for complex heritage detailing.
5) Does frame width represent sash thickness or visible border?
Use the border that reduces the clear glazing area. If you need glass size inside rebates, use the rebate-to-rebate dimensions instead and set frame width to zero for that scenario.
6) Can I export only the latest calculation?
Exports include saved rows from this session, with the newest at the top. If you want one row, clear saved rows, run a single calculation, then download CSV or PDF.