Free Live Calculators

Cushion Fabric Calculator: Box, Knife-Edge & Round Cushions

Calculate fabric for box, knife-edge, and round cushions. Covers sofa, chair, bench, and outdoor pads with seam allowances, piping, and multiple quantities.

Finished cushion width

Finished cushion length

Depth of the finished cushion

Number of cushions to make

Add 10% to your order for cutting errors and re-cuts. For patterned fabric, add one full pattern repeat per fabric width.
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How to Use This Calculator

  1. 1

    Select cushion type

    Choose Box Cushion for sofa, chair, bench, or outdoor seat cushions with a side boxing strip. Choose Knife-Edge for flat throw pillows and simple covers. Choose Round Cushion for circle-shaped cushions.

  2. 2

    Enter finished cushion dimensions

    Enter the finished size — not the cut size. The calculator adds seam allowances automatically. For a box cushion, enter width, length, and thickness (the depth of the cushion). For round, enter the finished diameter.

  3. 3

    Set quantity and fabric width

    Enter how many cushions you need. Select your fabric bolt width — 54" is most common for home décor and upholstery fabrics. The calculator optimizes the layout across your fabric width.

  4. 4

    Choose seam allowance

    ½" is standard. Use ⅝" for upholstery-weight fabrics. The calculator adds seam allowance to all cut dimensions.

  5. 5

    Toggle piping if needed

    Enable the piping option if your cushion design includes welting or piping around the seams. The result shows face fabric and piping strip yardage separately.

What Each Value Means

Finished Size (inches or cm)
The dimensions of the completed cushion — what you measure before it's stuffed, or the size of the insert you're covering. Do NOT include seam allowances in this measurement; the calculator adds them.
Boxing Strip (inches or cm)
The strip of fabric that runs around the sides of a box cushion, giving it depth. Cut as 4 separate pieces (2 long + 2 short) or one continuous strip. Height = cushion thickness + 2 × seam allowance.
Seam Allowance (inches or cm)
The extra fabric beyond the finished edge where stitching occurs. ½" is standard for most home sewing. Always add seam allowance on BOTH sides of each dimension — the calculator does this automatically.
Piping / Welting (linear yards/metres)
Fabric-covered cord sewn into the seam between panels and boxing strips. Adds a professional finish. The fabric is cut in 1.5"-wide strips, wrapped around the cord, and basted before assembly. The calculator shows extra yardage needed for piping strips.

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Frequently Asked Questions

How do I calculate fabric for a box cushion?
You need 6 pieces: 2 panels (top + bottom) and 4 boxing strips (2 long, 2 short). Panel cut size = finished width + 1" × finished length + 1" (for ½" seam allowance all around). Boxing strip height = thickness + 1". Calculate each piece, arrange on your fabric width, and sum the running length.
How much fabric do I need for a 24" × 24" × 4" sofa cushion?
Approximately 1.5–2 yards of 54" fabric. Two 25" × 25" panels fit side by side on 54" fabric. Boxing strips add about 0.5 yard. Add 10% for cutting safety = about 2 yards total.
What seam allowance should I use for cushions?
Use ½" (1.3 cm) for most home sewing projects. Use ⅝" (1.6 cm) for upholstery-weight fabrics that fray easily. Use 1" for very heavy or thick fabric like canvas or outdoor fabrics. The calculator adjusts all cut dimensions based on your selected seam allowance.
How do I calculate piping or welting fabric?
Piping strips are cut 1.5" wide. For a box cushion, total piping length = 4 × (width + length) for both top and bottom seams, plus about 12" per cushion for joining. Divide by your fabric width to find how many 1.5" strips you need. The calculator does this automatically.
How much fabric for outdoor chair cushions?
A standard 20" × 20" × 4" outdoor seat cushion needs about 1.5 yards of 54" fabric. For a set of 4 outdoor chair cushions (same size), expect 5–6 yards including piping. Use the calculator with your exact measurements for a precise number.
How do I calculate fabric for a round cushion?
Cut each circle from a square: cut square size = diameter + 1" (for ½" seam). Two squares per cushion. If adding a boxing strip, cut length = circumference (π × diameter) + 12" for joining × boxing height. The calculator handles this automatically.
Can I use the same fabric calculation for outdoor and indoor cushions?
Yes — the fabric geometry is identical. The difference is in the fabric type you buy: outdoor fabrics (Sunbrella, Olefin, solution-dyed acrylic) are sold at the same widths (54"–60") and cut the same way. The calculator works for all fabric types.
How much extra fabric should I buy for cushions?
Always add 10% above the calculated amount for cutting errors, miscuts, and re-cuts. For patterned fabric, add one full pattern repeat per fabric width to allow for pattern matching. All fabric for a project should be bought at once from the same dye lot.