Measure the chair’s inside seat width left-to-right and inside depth front-to-back on the bare frame, not the worn cushion, then match those numbers to a 16 by 16 inch cushion.
A tape measure works fine, but measure the frame, not the old cushion. A flattened insert can sit an inch or more smaller than the frame opening, so a 16 x 16 cushion ordered from those dimensions often arrives too small. Measure once, correctly, and every replacement after that drops in without a return.
Start With The Frame, Not The Old Cushion
The frame is the only true reference, because unlike a compressed cushion it does not change shape. Lay the tape across the wide points of the seat structure and write each number down before you touch a catalog.
If your seat has arms, take the width between the inside faces of those arms, not the outside edges. With no arms, measure from the outside frame edge across. Depth always runs front to back, from the front lip of the seat to where the seat surface meets the backrest.
A 16 x 16 cushion means 16 inches wide by 16 inches deep. If your frame is not perfectly square — and many are not — measure at the front and again at the back and note the difference.
How Much Room Should You Leave For Fit?
The allowance depends on your chair, not a universal rule. One guide suggests adding about an inch to width and depth so the cushion sits snug with slight overhang; another suggests subtracting a quarter to half inch from a tight opening so the insert does not buckle upward when you sit.
Tight metal or wicker frames with close arms do better with the subtract approach, because a cushion filling every millimeter will mushroom at the seams. Open wood or slatted frames with roomy arm clearance usually take the add-an-inch approach, keeping the cushion from sliding when someone gets up. Decide once, then hold that number steady across the whole set.
Thickness And Back Cushion Math
Thickness is a separate measurement and it changes your back cushion size. Pinch the tape at the thickest point, top to bottom, at full loft — not squashed flat.
For a back cushion, run the tape from the top of the seat surface to the top of the backrest for back height. Subtract your seat cushion thickness from that number before ordering, so the back panel does not ride up over the top rail. Measure back width the same way as seat width: left to right across the inside of the backrest frame.
| Cushion Part | Where The Tape Goes | Target For A 16 x 16 Seat |
|---|---|---|
| Seat width | Inside frame edge to inside frame edge, between armrests | 16 inches |
| Seat depth | Front seat lip to where seat meets the backrest | 16 inches |
| Fit allowance | Added to or subtracted from the frame numbers above | Add about 1 inch, or subtract 1/4 to 1/2 inch on tight frames |
| Cushion thickness | Thickest point, top to bottom, at full loft | Measure only — do not assume |
| Back cushion width | Inside of backrest frame, left to right | Match seat width unless the chair tapers |
| Back cushion height | Seat surface to top of backrest, minus seat cushion thickness | Shorten by your seat cushion’s loft |
Curved Seats And The Measurement Mistakes That Cost You
A square cushion only works on a square seat. Curved, rounded, tapered, or heavily armed seats may need a custom cut, and a nominal 16 x 16 insert can gap or hump no matter how carefully you measured.
For an irregular seat, make a template: trace the seat outline on cardboard, cut it out, and set it in the chair before ordering. If the template rocks or leaves a gap at the corners, a stock square cushion will too.
The mistakes show up predictably: measuring a flattened old cushion instead of the frame, skipping armrest clearance, missing a backrest that narrows toward the top, and forgetting thickness when sizing a back piece. Checking all four saves a return label.
Once your numbers are locked in, compare cushions that list their dimensions rather than a “fits most chairs” label — our tested roundup of the best 16 x 16 outdoor chair cushions is sorted by exactly these measurements. Ballard Designs publishes a similar walkthrough for a second opinion on the frame-first approach to measuring outdoor cushions.
FAQs
Do I measure the chair or the old cushion?
Measure the chair frame. An old cushion has been sat on, rained on, and compressed for seasons, so it usually reads smaller than the opening it came from. Frame measurements stay stable, so the new insert fits the first time.
What if my chair seat is not a perfect square?
Measure width at both the front and back, and depth at both the left and right sides. Write down the range, then match a cushion to the larger figure. Seats that narrow toward the back need the front width as your working measurement.
Should the cushion overhang the frame or sit inside it?
Both are normal, depending on the chair. Roomy frames with open arms handle a slight overhang well and it keeps the cushion from sliding. Tight frames with close-set arms do better with an insert that sits just inside the opening, which prevents buckling at the seams under weight.
References & Sources
- Ballard Designs. “Measuring Outdoor Cushions.” Covers frame measurement, seat depth, and back cushion height subtraction.
- Frontgate. “The Right Fit: How to Measure for Replacement Cushions and Furniture Covers.” Explains fit allowance and wider-point measurement practice.
- Wayfair. “How to Measure for Outdoor Cushions.” Supports thickness measurement and template method for irregular seats.
