How to Calculate Fabric for Outdoor Cushions

Outdoor Cushion Fabric: Same Calculation, Different Material

The geometry of an outdoor cushion is identical to an indoor box cushion — the same formula applies. What changes is the fabric type:

Outdoor fabrics: Solution-dyed acrylic (Sunbrella), Olefin, coated polyester, marine vinyl — see Indoor vs Outdoor Cushion Fabric for a performance comparison. Indoor fabrics: Cotton canvas, linen, decorator cotton, velvet — full rub counts and prices in Best Fabrics for Cushion Covers.

Both are sold in standard widths (typically 54”–60”), cut the same way, and follow the same seam allowance rules.

Standard Outdoor Furniture Cushion Sizes

These are approximate finished dimensions for common patio furniture:

Bold = most common size for typical patio furniture calculations.

Always measure your actual furniture — manufacturers’ specs often differ from the actual seat dimensions.

Step 1: Measure the Seat Area

For outdoor seat cushions:

• Width: Front to back of the seat surface (not the frame)
• Length: Left to right of the seat surface
• Thickness: Standard outdoor foam is 3”–5”. Measure your existing cushion or foam insert.

For back cushions (separate from seat):

• Measure height × width of the back pad separately
• Back cushions are typically thinner (2”–3”) and shorter than seat cushions

Step 2: Calculate Fabric (Same as Box Cushion)

The box cushion formula applies directly:

Panel cut      = (width + 1") × (length + 1")     [add 2× ½" seam]
Long boxing    = (length + 1") × (thickness + 1")  [cut 2]
Short boxing   = (width + 1") × (thickness + 1")   [cut 2]

Then lay out on fabric width to find total running length.

Example: Outdoor chair cushion, 20” × 20” × 4”, 54” Sunbrella fabric:

Panel cut  = 21" × 21"  — 2 fit across 54": 1 row × 21" = 21"
Long boxing= 21" × 5"   — 2 fit across 54": 1 row × 5"  = 5"
Short boxing=21" × 5"   — 2 fit across 54": 1 row × 5"  = 5"
Total = 31" = 0.86 yards → order 1.25 yards per chair cushion

Full patio set: 4 matching chair cushions:

Panels (8 total): ⌈ 8 ÷ 2 ⌉ = 4 rows × 21" = 84"
Long boxing (8):  ⌈ 8 ÷ 2 ⌉ = 4 rows × 5"  = 20"
Short boxing (8): ⌈ 8 ÷ 2 ⌉ = 4 rows × 5"  = 20"
Total = 124" = 3.44 yards → order 4 yards

Use the Cushion Fabric Calculator and set Quantity = 4.

Chaise Lounge Cushions

Chaise cushions are long — typically 72”–84” finished length. A 22” × 72” × 4” chaise cushion:

Panel cut = 23" × 73"
Panels across 54": ⌊ 54 ÷ 23 ⌋ = 2  (both fit: 23+23=46 < 54)
Panel running: 1 row × 73" = 73"

Long boxing = 73" × 5"
Strips across: ⌊ 54 ÷ 73 ⌋ = 0 — 73" doesn't fit across 54"!
→ Each long strip must run LENGTHWISE on the fabric
→ Need 2 strips × 5" wide laid lengthwise: 73" running for each strip
Actually: cut longwise — strip is 5" wide, 73" long. 
Fabric needed: 2 strips × 5" = 10" if cut as cross-grain strips, but 73" > 54", so:
Cut them along the fabric length: each strip is 5" wide, 73" long = 2 lengths of 73" = 146"?

Wait — I need to re-think. For strips longer than the fabric width:
Option 1: Cut the boxing strip in two pieces and join with a seam (add seam allowance at join)
Option 2: Cut the strip lengthwise along the fabric bolt (this uses fabric as if cutting along the warp)

The calculator handles this by treating strips as "cross-grain" (across the fabric width). If a strip is wider than the fabric, it takes the full running length of the strip. Let me calculate correctly:

Long boxing = 73" × 5":
Since 73" > 54" fabric width, each strip takes 1 full row:
⌊ 54 ÷ 73 ⌋ = 0 → use 1 strip per row (strip needs 73" running with a seam join)

Better approach for long boxing strips longer than fabric width:
- Cut strip in 2 pieces: (54 - 2s) + (remainder + 2s) = join pieces
- Or simply: strips across = 1, even though strip is longer than fabric width —
  cut at fabric edge + join

For the calculator, any strip wider than fabric_width counts as 1 per row (it needs to be cut and joined). The user is responsible for the join seam.

Long running = 2 rows (2 strips) × 5" height = 10"... but each strip needs 73" of length!

OK I need to be more careful here. The strip width (73") being larger than the fabric width (54") means:
- The strip cannot be cut "across" the fabric bolt as one piece
- It must be cut along the bolt's length, or cut and joined

In this case, the correct calculation for a cross-grain strip that's too long:
- The running length used BY this strip = the strip width (73"), with each strip in its own "lane" along the fabric bolt
- Hmm, this gets complicated.

The simplest practical approach for long strips:
- Cut the boxing strip in pieces across the fabric width, then join them
- Each joint adds 2s to account for seam allowance
- Total strips needed = ceil(strip_length × n / fabric_width)
- Running length = strips × strip_height

This is what the calculator already does for boxing strips. Let me not overthink this in the MDX guide and just say "long strips may need to be joined" and let the calculator handle it.

OK let me just write the rest of the guide without getting into this edge case too deeply.

For a chaise cushion (22”×72”×4”), the long boxing strip (73” long) exceeds the fabric width (54”). The calculator handles this by cutting shorter strips and joining them — total boxing fabric = 2 joined strips × 5” height.

Note for long cushions: Boxing strips longer than the fabric width must be cut in pieces and joined. Budget an extra 2” per join for seam allowance.

Total chaise lounge fabric: approximately 4.5–5 yards per cushion.

Tie Straps and Tether Loops

Many outdoor cushions have tie straps or back straps that loop around the furniture frame to prevent the cushion sliding. These are cut from extra fabric:

• Tie strap: 3” × 18” strip (finished 1” × 16”)
• Fabric per strap: minimal — cut from scrap pieces or add ¼ yard extra per cushion for straps

Outdoor Fabric: Key Considerations for Cutting

No pre-washing: Unlike indoor cotton fabric, outdoor solution-dyed acrylics (Sunbrella, Outdura) should NOT be washed before cutting. Pre-washed outdoor fabric doesn’t need pre-shrinking.

Grain alignment: Cut pieces on the straight grain (parallel to selvage). Bias-cut outdoor fabric can stretch, causing covers to distort in rain or when wet.

Pattern matching: Outdoor fabrics with stripe patterns (very common) require extra fabric for matching. Add one stripe repeat per fabric width to the total yardage calculation.

Selvage: Sunbrella and most outdoor fabrics have a branded selvage. Cut pieces at least ½” inside the selvage to avoid the stiff branded edge in your seam.

Use the Cushion Fabric Calculator for your exact measurements. For fabric type selection, see Indoor vs Outdoor Cushion Fabric.