Cushion cover sizes in the UK follow common standards, but variations between brands, retailers, and product lines create confusion. Buying covers that do not fit your inserts leads to baggy, underfilled cushions or overstuffed covers that strain at the seams. Understanding how sizing works across different cushion types helps you order confidently online and avoid the hassle of returns.
Standard UK Square Sizes
The most common UK cushion cover sizes in centimetres are 40, 43, 45, 50, and 55. The 45 cm square is the dominant standard, stocked by virtually every retailer and fitting the majority of sofa cushion inserts. When a product listing says “standard size” without specifying dimensions, it almost always means 45 cm.
The 40 cm cover suits smaller accent cushions on armchairs, window seats, and single beds. The 50 cm and 55 cm covers suit larger sofas, deep sectionals, and king or super king beds where smaller cushions look undersized. Euro square covers measure 65 cm and are used primarily as bed shams propped against the headboard behind sleeping pillows.
Some UK retailers still list cushion sizes in inches. The common conversions are: 16 inch = 40 cm, 17 inch = 43 cm, 18 inch = 45 cm, 20 inch = 50 cm, 22 inch = 55 cm, and 26 inch = 65 cm (Euro). When buying from retailers that list both metric and imperial, always use the centimetre measurement because rounding during conversion can create a 1 to 2 cm discrepancy.
Rectangular Sizes
Rectangular cushion covers come in less standardised sizes than squares. The most common rectangular sizes are 30 cm x 50 cm (lumbar), 40 cm x 60 cm (breakfast or boudoir), and 50 cm x 70 cm (large rectangular). Lumbar covers (30 x 50) are the most popular rectangular size and sit well on sofas for lower back support and visual contrast against square throw pillows.
Rectangular inserts are less widely available than square inserts, so check insert availability before committing to an unusual rectangular cover size. Some niche cover sizes (35 x 55, 45 x 65) may require custom-made inserts or creative substitution. Bolster covers have their own sizing system based on diameter and length rather than width and height, adding another dimension to consider.
Oubonun Throw Pillow Inserts
The Insert-to-Cover Sizing Rule
Always buy inserts 5 cm larger than your cover in each dimension. A 45 cm cover needs a 50 cm insert. A 30 x 50 cm rectangular cover needs a 35 x 55 cm insert. The oversized insert pushes into every corner of the cover, creating the full, plump appearance that makes cushions look professionally styled.
Same-size inserts (45 cm insert in a 45 cm cover) leave the corners empty and the cover looking saggy. The visual difference between a correctly oversized insert and a same-size insert is dramatic, and this single detail separates cushions that look cheap from ones that look expensive regardless of the cover quality.
Going 7 cm or more oversized creates the opposite problem: the cover strains visibly, the zip struggles to close, and the cushion looks overstuffed and misshapen. Stick to the 5 cm rule for consistent results across all sizes.
Measuring Existing Inserts
Remove the insert from its current cover before measuring. Lay the insert flat on a table without pressing down. Measure edge to edge at the widest point (inserts round out slightly, so the centre is wider than the sewn edges). Record both width and length for rectangular inserts.
For worn inserts that have lost their shape, measure the sewn edge dimensions rather than the current lofted dimensions. A 50 cm insert that has flattened to 48 cm across the surface is still a 50 cm insert because the sewn edges define its size. Buy your cover based on the sewn dimensions minus 5 cm (so a 50 cm insert gets a 45 cm cover, even if it currently appears smaller).
Specialty Cover Sizes
Floor cushion covers range from 60 cm to 100 cm square and are significantly larger than sofa cushion covers. Floor cushion inserts are thick (10 to 20 cm) and dense, requiring covers with gussets (side panels) rather than flat two-panel construction. A flat cover on a thick floor cushion insert distorts badly because the fabric cannot accommodate the depth.
Outdoor cushion covers follow the same general sizing as indoor covers but may use slightly different standards depending on the furniture manufacturer. Many outdoor furniture brands sell proprietary replacement covers sized specifically for their seats and backs. Check your outdoor furniture brand’s specifications before buying generic covers, as even a 2 cm difference creates a poor fit on structured outdoor seating.
Oubonun Throw Pillow Inserts
Buying Covers Online
Online shopping for cushion covers requires careful attention to dimensions because you cannot check the fit physically. Always verify: the exact measurements in centimetres (not just “standard”), the closure type (zip or envelope), and the fabric composition. Read reviews specifically mentioning sizing accuracy, as some overseas sellers list nominal sizes that differ from actual measurements by 2 to 3 cm.
When ordering from international sellers (common on Amazon and Etsy), confirm whether dimensions are inside measurements (the actual cover opening) or outside measurements (including seam allowances). A cover listed as 45 cm on the outside may only measure 42 to 43 cm on the inside, which changes the insert size you need. UK retailers typically list the inside measurement, but this is not universal. Our pillow care guide covers what to check before first use, including pre-washing to account for any shrinkage.
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