How to Measure Adirondack Chair Cushions: Seats, Fan Backs and Slat Gaps

The Adirondack is two measuring jobs wearing one chair. The seat is the most forgiving cushion target in outdoor furniture — a flat, unobstructed deck where a close fit just works, which is why stock 20-inch squares cover so many of them. The back is the opposite: a tall, reclined fan of slats that angles away from vertical, tapers as it rises, and offers the only strap anchors through the gaps between boards. Measure the seat casually and you will be fine; measure the back casually and the cushion will not fit, will not stay, or both.

The method underneath is the standard protocol — seam to seam on the old cushion or frame-first when it is gone, foam thickness read at the seam line, every number confirmed to tolerance before cutting (±½” on custom dimensions, ±¾” over 36 inches). The complete walkthrough lives in how to measure outdoor cushions; this page is the Adirondack layer. For ordering, the custom Adirondack chair cushions page carries the seat-and-back preset with the outdoor fabric tiers this chair lives in.

Step 1: Measure the Seat Deck — Width Twice, Depth Once

Adirondack seats taper more than most chairs because the wide-arm design narrows toward the back.

1. Width at the front edge of the seat deck, between the arms.
2. Width at the back, where the seat meets the back frame. If the two differ by more than half an inch, you need a trapezoid cut — record both numbers, front and back, as separate widths.
3. Depth from the front edge to where the seat meets the back frame. The reclined geometry hides the junction lower than it looks; measure the flat deck only, tape level.

Most seats land in the 19–21 inch range with 20 × 20 as the de facto standard, and oversize “king” Adirondacks take 22–24 inch squares. If your deck measures within half an inch of a stock size, the standard cushion wins on price and availability; outside that band, the custom route is the one that actually fits (the full sizing context).

One Adirondack quirk to note while you are down there: the seat deck often carries a slight backward slope as part of the chair’s ergonomics. Do not correct for it in the depth — the foam spec can be tapered later (Step 3) — just note it.

Step 2: Measure the Fan Back — Height First, Then the Taper

Back cushions come in two styles, and they measure differently:

• – Short back (lumbar) pads, roughly 20 × 12 to 20 × 14: lower-back coverage that fits any back height. Measure the width where the pad will sit — usually the widest point below mid-back — and a 12–14 inch height. This is the safest upgrade when the back height is unknown or the chair is headed for gifting.
• – Full-height back cushions, 20 × 24 up to 21 × 30: total coverage up the fan. Measure height from the seat deck to the top slat, minus 2–3 inches so the cushion does not overhang the crest rail, and width at the widest point the cushion will reach — because the fan tapers, a full back cushion cut as a rectangle will overhang the slats on both sides near the top.

The tailored move on full backs is a tapered cut that follows the fan: record the width at the bottom of the cushion’s run and the width at the top, exactly like the seat trapezoid but vertical. It reads as built-in rather than strapped-on, and it is a cutting detail, not a redesign — tapered fan-back cuts are routine on our floor.

Step 3: Respect the Recline — Geometry Before Comfort

The Adirondack back leans away from vertical by design, and that angle affects three decisions:

• – Seat thickness. The chair’s recline is calibrated for a cushioned seat; 2–4 inches is the working range, with thicker pads pushing you further forward in the arc. On folding resin Adirondacks with slightly crowned seats, stay at 2–3 inches or the geometry pushes you past the recline.
• – Back cushion thickness. Every inch of back pad moves you that far forward off the designed posture. 2–3 inches is the range that adds comfort without re-engineering the chair.
• – The seat’s backward slope. Where the deck slopes, the foam can be tapered a quarter to half inch from front to back to level the sitting position — an option stock cushions never offer, and worth specifying on chairs you expect to sit in for hours.

Step 4: Draw the Slat-Gap Map

Back cushions attach through the gaps between slats, so the map of those gaps is the fit:

1. From the seat deck upward, measure the height of each gap between slats.
2. Note gap widths — poly-wood (HDPE lumber) chairs run wider gaps than wood, and straps need enough length to wrap and fasten behind.
3. Decide which two gaps the straps will use, and record them by height from the deck.

Straps landing on solid wood instead of a gap is the number-one back-cushion fit failure on Adirondacks — a cushion can be dimensionally perfect and still not stay put. Five minutes with a pencil converts that risk into a spec.

Step 5: Handle the Special Cases

• – Vintage and handmade chairs: pre-standardization seats run wider, deeper, or rectangular rather than square; tall backs pass 30 inches, which no stock cushion covers. Full custom territory, measured as above.
• – King Adirondacks: measure to the bigger deck and match the nearest standard square, or go custom for a one-piece seat-and-back unit.
• – Double Adirondacks (tête-à-tête, settees): two seat cushions plus one long or two separate backs. Measure the combined seat deck — often past 48 inches — and treat the long pad as a bench piece (bench cushion measurements covers the over-48-inch tie rules).
• – Ottoman pairings: roughly 18–20 inch squares, 2–3 inches thick; order in the same fabric run so the set matches.

Common Adirondack Measuring Mistakes

Mistake	What goes wrong	The fix
One seat width recorded	Trapezoid deck cut as rectangle; gaps at the arms	Width at front and back; both recorded
Depth measured down the slope	Cushion overhangs the front edge	Flat-deck footprint, tape level
Back height measured to the crest rail	Cushion overhangs the top on every recline	Height minus 2–3 inches
Back cut as a rectangle	Overhangs the tapering fan near the top	Bottom and top widths; tapered cut
Straps ordered without the map	Roots land on solid wood; cushion slides	Slat-gap heights from the deck up
Thickness by comfort alone	Recline pushes you forward out of the design	2–3 inches back, 2–4 seat; taper for slope

Adirondack Cushion Cheat Sheet

Measurement	What to record	Typical range
Seat width (front / back)	Both; trapezoid if >½” apart	19″–21″ (20 × 20 standard)
Seat depth	Flat deck, front to junction	18″–21″
Seat thickness	Seam to seam	2″–4″
Back style	Short lumbar or full height	—
Back height	Deck to top slat, minus 2–3″	24″–30 full; 12–14 short
Back width (bottom / top)	Both for a tapered fan cut	20″–21″
Slat-gap map	Height of each gap from the deck	3–5 gaps typical
Strap points	Two gaps, by height	—

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