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Curtain Panel Cut Length: Finished Drop, Hem, and Header Allowances

Sew Measure · 2026-10-27

Curtain panel cut length is a vertical stack of labeled allowances: the finished drop you want to see on the window, plus the fabric consumed by the bottom hem, plus the fabric consumed by the top treatment (header or ruffle, rod pocket or casing, and any turn-under). Optional pattern-repeat rounding comes after that sum, and shop rounding to purchase yards is a separate sensitivity step—not part of the cut-length identity. This worksheet does not size fullness or cut width; width and gathering belong in width planners such as the curtain fabric tool. Here the only question is how long to cut each panel before you sew.

Industry sewing guidelines and education worksheets agree on the structure even when their sample inch totals differ: measure the finished length first with the rod installed, then add explicit top and bottom allowances. The Home Sewing Association guideline for rod-pocket curtains states a compact form: to finished panel length, add 3 inches for the header, the rod circumference plus 1 inch for the pocket opening, 1/2 inch for finishing the casing, and 2 inches for the lower hem—summarized as 6 1/2 inches plus the rod circumference. BERNINA's yardage worksheet for valances doubles the pocket and header heights in the cut (because those sections are folded), then adds bottom hem depth, turn-under, and a small ease. Pick one construction recipe, label every term, and do not mix recipes mid-calculation.

What each length term means

Finished drop (finished length) is the length of the hanging panel as you want it to read on the window—typically from the top of the treatment's visible top edge down to the hem line, or from below the rod to the hem if your pattern defines finished length that way. Install the rod before you measure. Bottom hem allowance is the fabric length consumed by the hem fold(s), not the finished hem depth alone: a double 3-inch hem consumes about 6 inches of fabric; a double 4-inch hem consumes about 8 inches. Header or ruffle is fabric above the rod pocket that stands or gathers above the rod. Rod-pocket (casing) depth must clear the rod; guidelines often size the pocket from rod circumference or at least roughly twice the rod diameter. Turn-under is a small finishing fold at the top raw edge before the casing is formed. Pattern repeat extra is optional: for patterned cloth, you may round the cut length up to a whole number of vertical repeats so motifs align across widths.

Cut length per panel, before purchase rounding, is:

cut length = finished drop + bottom hem allowance + top/header/rod-pocket stack (+ optional repeat rounding)

Purchase yards per panel = cut length ÷ 36, then multiply by panel count and round the bolt purchase. That shop step is sensitivity, not a hidden part of the cut identity.

Worked example with stated assumptions

Construction A follows the Home Sewing Association rod-pocket guideline (8.150). Assumptions:

  • Finished panel length (drop): 84 in
  • Header: 3 in
  • Rod circumference: 3 in (measure the installed rod; a roughly 1-inch-diameter rod is near π inches around—use a cloth tape on the actual rod)
  • Rod-pocket opening add-on: 1 in (per the guideline's "circumference + 1 inch" pocket term)
  • Casing finish / turn-under: 0.5 in
  • Lower hem allowance: 2 in (as stated in that guideline's compact list)
  • Pattern repeat: none (solid fabric)

Top-and-bottom add-ons per the compact form = 6.5 + rod circumference = 6.5 + 3 = 9.5 in.

Cut length = 84 + 9.5 = 93.5 in.

Check by parts: 84 + 3 (header) + 3 (circumference) + 1 (pocket opening) + 0.5 (casing finish) + 2 (lower hem) = 93.5 in. Same result.

Construction B restates a folded pocket/header style similar to BERNINA's valance cut-length table, with a deeper double bottom hem common on full-length panels. Assumptions:

  • Finished length below the rod: 84 in
  • Rod pocket depth: 1.5 in → fabric for pocket fold = 2 × 1.5 = 3 in
  • Header height: 2 in → fabric for header fold = 2 × 2 = 4 in
  • Bottom hem fabric: 8 in (double 4-inch hem)
  • Turn-under: 0.5 in
  • Ease: 0.5 in
  • Pattern repeat: none

Cut length = 84 + 3 + 4 + 8 + 0.5 + 0.5 = 100 in.

The two constructions differ because the hem depth and the folding convention differ—not because the window changed. Choose the recipe that matches how you will sew the top and hem, then stick to it for every panel in the set.

Optional pattern-repeat rounding

If the fabric has a vertical repeat of 12.5 in and you are using Construction A's 93.5 in cut, divide 93.5 ÷ 12.5 = 7.48. Round up to 8 repeats: 8 × 12.5 = 100 in cut length per panel. That extra 6.5 in is motif alignment insurance, not hem. Solids and non-repeating textures skip this step. When you seam multiple widths into one panel, each width after the first still needs the same cut length so the motif meets at the seams; the pattern repeat allowance tool is the place to pressure-test that math before you buy.

Purchase rounding stays optional

For one panel at 93.5 in: 93.5 ÷ 36 ≈ 2.597 yards. Two panels: ≈ 5.194 yards. A shop that sells in 1/8-yard increments might round a two-panel order to 5 1/4 yards; a bolt cut in 1/4-yard increments might go to 5 1/4 or 5 1/2 depending on store policy. Record the cut length first, then apply store rounding. Do not feed the rounded purchase yards backward into the hem math—that hides whether you are short on a single panel.

Preshrink washable fabric before the final cut if you will launder the curtains later; the Home Sewing Association guideline calls this out explicitly. Shrinkage after cutting shortens the finished drop even when the worksheet was correct.

Sensitivity: where the cut moves

Hold Construction A's structure and finished drop 84 in. Change only rod circumference:

  • 2 in circumference → add-ons 8.5 → cut 92.5 in
  • 3 in → cut 93.5 in (example)
  • 4 in → cut 94.5 in

Hold rod circumference 3 in and finished drop 84 in. Replace the 2 in lower hem with an 8 in double-hem allowance (keeping the same 3 + 3 + 1 + 0.5 top stack = 7.5 in): cut = 84 + 7.5 + 8 = 99.5 in. Hem depth is often the largest single swing after finished drop itself.

Change finished drop only, Construction A, rod circumference 3 in:

  • 63 in sill length → cut 72.5 in
  • 84 in → cut 93.5 in
  • 95 in floor-length with clearance plan → cut 104.5 in

Measure to the planned hem line (sill, apron, or floor with clearance), not to a guess from an old panel.

Failure modes and limits

Measuring before the rod is installed shifts the finished drop when the rod height changes. Mixing finished hem depth with hem fabric allowance under-cuts the panel (using 4 in of fabric for a double 4 in hem leaves you short). Mixing Construction A's single-listed pocket add-ons with Construction B's doubled pocket/header double-counts or under-counts. Treating purchase-yard rounding as part of cut length makes one panel look fine on paper while the second panel runs short after seams and matching. Fullness multipliers belong on cut width, not on cut length—multiplying the drop by 2× "for gathers" is a category error.

This guide does not choose lining offsets, interlining, blackout layers, or tab/ring-tape headings. Lined panels often cut lining slightly shorter so the face hem covers the lining hem; that is a second cut length, not a rewrite of the face formula. Ring-top or pinch-pleat tape headings replace the rod-pocket stack with a different top allowance from the tape manufacturer—swap the top stack, keep the finished drop and hem logic.

A practical routine

  1. Install the rod; measure finished drop to the planned hem line.
  2. Choose the top construction (rod pocket with header, tabs, ring tape, etc.) and write each top allowance in inches.
  3. Choose the bottom hem style; convert finished hem depth into fabric consumed (usually about 2× for a double hem).
  4. Sum finished drop + hem fabric + top stack = cut length; optionally round up to whole pattern repeats.
  5. Cut a paper or muslin test strip if the window is expensive fabric; confirm the hanging length before cutting the fashion goods.
  6. Convert cut length × panel count into purchase yards; apply store rounding last.
  7. Preshrink if the curtains will be washed; re-measure after pressing.

For width, fullness, and how many fabric widths to seam, leave this page and use a width-focused planner. Length mistakes and width mistakes look similar on the receipt and very different on the window.

Sources and method

AI-assisted writing with automated source, calculation and editorial checks. No hands-on testing or professional certification is claimed. Check the stated assumptions before applying this guide. Inch arithmetic above uses ordinary U.S. customary inches; convert consistently if you work in centimeters (1 in = 25.4 mm exactly per NIST).