How to Measure Patio Chair Cushions | The 3-Number Method

Measure the chair’s usable seating area in three dimensions: width, depth, and thickness, using a rigid tape measure.

Getting the right size for patio chair cushions comes down to three numbers: width, depth, and thickness. The mistake most people make is measuring the old cushion while it’s flattened or compressed, which gives you a replacement that fits like a deflated balloon. The better approach is to measure the chair frame itself, and this guide walks you through exactly where to put the tape.

The Standard Method: Width, Depth, and Thickness

The core method is consistent across every buying guide: measure three dimensions in a specific order so you don’t mix them up later. Always record them as width, depth (or length), and thickness (or height) — that consistent order prevents ordering mix-ups when you’re comparing options online.

• Width: Measure the seat from left to right across the widest point of the usable seating area.
• Depth: Measure from the front edge of the seat straight back to the back support.
• Thickness: Measure from the top of the seat surface straight down to the bottom, at the fullest point — do not compress the cushion or measure it while squished.

The most reliable reference is the chair frame’s usable inside space rather than an old cushion that has lost its shape. If you’re replacing cushions on a set, measure each piece individually rather than assuming the left and right cushions are identical — they often aren’t, especially on curved or sectional furniture.

Fit Allowance: Should You Add or Subtract?

Sources genuinely disagree on fit allowance, so here’s the honest version. Home Depot’s guide recommends adding about 1 inch to your width and depth measurements for a snug fit. Lowe’s buying guide, by contrast, advises subtracting about 1/4 to 1/2 inch from tight frame measurements to prevent bunching.

The real answer depends on your frame. If the chair has a deep recess where the cushion sits, subtract a little so the cushion drops in cleanly. If the cushion sits on top of a flat surface, adding an inch gives you a slightly fuller look without overhang. When in doubt, measure the existing cushion in its fully expanded state and compare it against the frame — that tells you which adjustment your particular chair needs.

Special Cases: Back Cushions, Chaises, and Wicker

Back cushions need a fourth calculation: measure the back width from left to right, then measure back height from the top of the seat to the top of the chair back. Here’s the catch — subtract the seat cushion’s thickness from your back height measurement, or the back cushion will sit too tall and look awkward.

For chairs with hinges or a bend between seat and back, measure each section separately at the break where the chair bends so the hinge aligns properly. Wicker and rattan frames require measuring inside edge to inside edge, and you’ll want to note whether the back corners are rounded or square, plus any cutouts or notches in the frame that could affect fit.

Don’t ignore arm clearance, frame lips, or tabletops — a cushion matching the nominal dimensions can still fail if arms pinch it or a table edge overlaps it. When you’re ready to buy, our tested roundup of 16 x 16 outdoor chair cushions covers the top-rated options that fit this common size.

Common Mistakes That Ruin the Fit

Most cushion failures come down to a handful of repeatable errors. Using a soft sewing tape instead of a firm one lets the tape bend or stretch, skewing your numbers by half an inch or more. Measuring the outer furniture dimensions instead of the usable inside space gives you a cushion that looks right on paper but doesn’t drop into the frame. And measuring a compressed cushion — one that’s been sat on for years — guarantees a replacement that’s too thin.

The fix for all three is the same: use a rigid tape measure, measure the frame’s usable interior, and take the thickness measurement on the cushion fully expanded, not squished. BBQGuys’ cushion measuring guide covers this method in detail, including how to handle rounded corners and chaise sections.