Cushion Types and Construction: Box, Knife-Edge & Round

The Three Main Cushion Construction Types

1. Box Cushion

What it is: A cushion with a top panel, a bottom panel, and a boxing strip that runs around all four sides, giving the cushion a defined depth.

Pieces required:

• Top panel × 1
• Bottom panel × 1 (sometimes split for a zipper opening)
• Long boxing strips × 2 (run along the length)
• Short boxing strips × 2 (run along the width)

Fabric required: Most of any cushion type — the boxing strip adds significant yardage on thick cushions.

What it looks like: A neat, rectangular cushion with clean 90° edges. The sides are clearly defined. Looks crisp and tailored.

Best for:

• Sofa and armchair seat cushions — see How Much Fabric for Sofa Cushions for full sofa yardage
• Outdoor furniture (patio, garden, poolside)
• Bench cushions (dining, garden, window seat)
• Any cushion that needs a defined height/thickness

Difficulty: Moderate. Requires careful measurement and precision at the corners where boxing meets panels.

2. Knife-Edge Cushion

What it is: Two fabric panels sewn together at the edges. No boxing strip. The cushion tapers to the stitched edge at all sides.

Pieces required:

• Top panel × 1
• Bottom panel × 1

Fabric required: Least of any cushion type — just two panels. No boxing to calculate.

What it looks like: Flat at top and bottom, with edges that pinch in to a sewn seam. If overstuffed, forms a “pillow” shape that puffs out. Classic throw-pillow look.

Best for:

• Decorative throw pillows
• Scatter cushions
• Any flat, decorative cushion
• Quick recovery projects (covering an existing insert)

Difficulty: Easy. Just two panels, one seam (or two seams if using a zipper). Ideal for beginners.

3. Round Cushion

What it is: Two circular panels, optionally with a boxing strip for depth.

Variants:

• Round knife-edge: Two circular panels only. Puffs up like a round pillow.
• Round box: Two circular panels + a continuous boxing strip running around the circumference.

Pieces required:

• 2 circular panels (each cut from a square)
• 1 boxing strip (optional, for round box variant) — cut as a long rectangle, then joined around the circumference

Fabric required: Moderate. Circles are cut from squares, so there’s inherent waste in the corners. Boxing strip adds length proportional to the diameter.

What it looks like:

• Without boxing: round, plump, decorative pillow
• With boxing: neat cylindrical cushion (like a meditation cushion or Ottoman footstool)

Best for:

• Meditation and floor cushions
• Decorative round pillows
• Drum-shaped Ottoman covers
• Pouffe re-covering

Difficulty: Moderate (without boxing) to Advanced (with boxing). Sewing around a circle requires clipping the seam allowance to avoid puckering. Boxing attachment requires even distribution of the strip around the circumference.

Construction Methods: Zipper vs No Zipper

With a Zipper

A zipper allows the cushion cover to be removed for washing, which is essential for cushions that will be used regularly (especially outdoor cushions that need laundering).

Zipper placement: Usually on the back boxing strip (the boxing strip at the back edge of the cushion). The back boxing strip is cut in two pieces with an overlap allowance of 1.5” for the zipper.

Zipper length: Standard is the full length of the back boxing strip. Use a zipper 1”–2” shorter than the back boxing dimension so the zipper pull doesn’t fall off the end.

Fabric adjustment: Adding a zipper does not significantly change the fabric calculation. The back boxing strip is cut as two pieces instead of one, but the total fabric is nearly the same.

Without a Zipper

For decorative cushions that won’t be washed, or cushions where the insert is permanent (glued foam, outdoor foam), no zipper is needed. Sew three sides, stuff or insert the cushion form, then slipstitch the fourth side closed.

Choosing Cushion Thickness (Boxing Height)

Thicker cushions require significantly more boxing strip fabric. A 6” thick sofa cushion uses nearly 50% more boxing fabric than a 4” cushion of the same width and length. For outdoor cushion fabric selection and UV performance, see Indoor vs Outdoor Cushion Fabric.

Fabric Width and Piece Layout

54” fabric is the most common width for upholstery and home décor fabrics. This width is critical for layout efficiency.

For standard sofa cushions (24”–26” wide):

• 2 panels fit side by side on 54” fabric (24+1” = 25 × 2 = 50 < 54”)
• This halves the running fabric length needed for panels

For bench cushions (48”–72” long):

• Long boxing strips often exceed half of 54” fabric — only 1 strip per row
• Short boxing strips (18”–20” wide) fit 2 per row

Use the Cushion Fabric Calculator to calculate exactly how pieces lay out on your fabric width.

See also: Cushion Fabric Formulas and How to Calculate Fabric for Box Cushions.