BEDDING GUIDE · 26 OCTOBER 2026 · BY LAVE STUDIO

How to measure for a custom silk duvet insert

A cover you already love is a good starting point for a new duvet. Check its dimensions before choosing the insert: a familiar size name does not always mean a familiar fit.

Why “King” is not enough

Size names are useful shortcuts, but the centimetres matter. For example, John Lewis lists a King duvet at 225 × 220 cm, while Dunelm’s bed linen guide lists a Kingsize cover at 230 × 220 cm. Both are sold under a King label. These are examples from the retailers’ own listings, not a universal sizing rule.

Lave’s UK standard options are below. If your cover differs, use custom dimensions rather than selecting the nearest name and hoping it will fit.

Measure the cover you will actually use

1. Read the label first. Look for the cover’s width and length, not the mattress dimensions or pillowcase measurements.
2. Lay it flat. Use a clean, dry cover in its usual washed condition. Smooth it gently without stretching the fabric.
3. Measure the usable pocket. Measure across from side seam to side seam, then from the head end to the foot end of the pocket. Exclude decorative borders, frills and the fastening flap beyond the space the insert occupies.
4. Check both measurements again. Write them down as width × length in centimetres. If the label and tape measure disagree, check with the cover’s maker or ask us before ordering.

Do not add extra centimetres simply to make the duvet look fuller. Choose a filling amount for that preference. If the cover is unusually shaped or you are uncertain about its construction, send us the measurements and a photo before buying.

Keep width and length in the right order

Width runs across the bed; length runs from head to foot. A 230 × 220 cm cover would normally call for an insert entered as 230 cm wide and 220 cm long. Do not enter mattress measurements: they describe a different object.

For a cover labelled in inches, multiply each measurement by 2.54 to convert to centimetres. For example, 90 × 90 inches is 228.6 × 228.6 cm. Keep the converted dimensions rather than rounding them to a UK size name.

Choose size and filling separately

Once the dimensions are settled, choose how much silk filling you want. Lave offers Light at 150 g/m², Medium at 250 g/m² and Warm at 400 g/m². A larger insert contains more silk at the same filling per square metre; it has more area to fill. Our fill-weight guide explains the calculation and the difference between filling weight and a warmth rating.

The insert has long-filament mulberry silk filling inside a cotton shell. Your removable cover is separate. Choosing custom dimensions changes the size; it does not add a cover or change the filling material.

Before you order

• Confirm the cover’s usable dimensions and the width/length order.
• Check that the measurement units are centimetres.
• Choose the filling for your preference, separately from the size.
• Read the delivery and returns information, including the terms for custom dimensions.

Published by Lave Studio, which sells made-to-order silk duvet inserts. Retailer size examples were checked on 26 October 2026; check your own cover before ordering.