Bedding specifications
GSM vs Thread Count: Read the Right Number
GSM and thread count answer different questions. GSM is mass per area. Thread count describes the number of yarns running in both directions in woven fabric. You cannot convert a 300 GSM material into a 300 thread count fabric.
With duvets, there is another complication: GSM may describe the filling rather than the cloth. Find the noun beside the number before comparing it.
The same unit can describe different parts
| Label | What is being measured | What remains unknown |
|---|---|---|
| Fabric GSM | Grams in one square metre of cloth | Fibre, weave, finishing and how it feels |
| Fill GSM | Grams of filling per square metre of duvet | Shell and cover weight, finished warmth and fit |
| Thread count | Lengthwise plus crosswise yarns in a defined area of woven cloth | Filling quantity or overall bedding quality |
| TOG | Thermal resistance | How substantial the fabric or duvet feels |
A heavyweight fabric and a duvet with a high fill GSM are not the same thing. One describes cloth; the other describes what is placed inside the shell. A product page should make that distinction easy to see.
Use GSM to understand scale
If a duvet lists fill GSM and its dimensions, you can make a useful approximate fill-mass calculation. YumeFeel King is 2.85 × 2.50 metres. Its nominal area is 7.125 square metres. Cloud's 800 g/m² specification gives approximately 5,700 grams of filling across that area.
King Cloud: fill only
2.85 m × 2.50 m × 800 g/m²
≈ 5,700 g of filling
Nominal rectangle calculation. It excludes shell, cover and other components; production details can affect the finished amount.
The same size at Air's 140 g/m² is about 1,000 grams of filling. That comparison explains two different builds within microfiber. It does not establish that any material with more grams must be warmer or better than every other filling.
A larger duvet can contain more fill without a higher GSM
This is the comparison that often catches people out. Keep Cloud’s listed 800 g/m² the same and change only its nominal size: Queen is 2.45 × 2.50 m, or 6.125 m²; King is 2.85 × 2.50 m, or 7.125 m². The calculation gives about 4.9 kg and 5.7 kg of filling respectively. The extra 0.8 kg belongs to the extra area. It does not make the King specification a higher-GSM grade.
For example, a listing that says only “duvet weight 5 kg” does not tell you how much of that weight is filling. Ask: “Is this fill weight, finished duvet weight, or packaged shipping weight?” That answer matters more than adding a decimal place to a calculation based on the wrong quantity.
Thread count belongs to woven cloth
A duvet's shell may have one thread count and the removable cover another. You do not add them together. Royal's 400 thread count cotton batiste shell and 300 thread count cotton percale cover remain two separate fabrics.
CottonWorks, from Cotton Incorporated, recommends examining fibre, yarn, construction and finish rather than relying on thread count alone. Those details help explain why two fabrics with the same number can feel different.
Compare like with like
Fill GSM is most helpful when you know which filling and construction it describes. Thread count is most useful when you also know the fibre, weave and yarn details. Neither should be used as a shortcut to infer durability, cooling or luxury without more information.
Be especially careful with unlabelled numbers. A large “900” near a down duvet may refer to fill power, not GSM or thread count. A seller should identify the measurement and component clearly enough that you can compare it.
Which number should decide the purchase?
Start with the outcome you want. For less warmth, look at the warmth specification. For coverage, read width and length. For a fabric feel you enjoy, look at the cover's material and weave. For a substantial insert, understand filling quantity and construction together.
Use the thread-count guide for shell and cover fabrics, or the TOG guide for warmth. The right number is the one measuring the thing you are trying to change.
YumeRest is YumeFeel’s bedding journal. Product examples use published specifications; this guide does not claim independent hands-on testing or a universal ranking.
