Fabric Weight (GSM ↔ oz/yd²)
Convert fabric weight between metric and imperial.
Type the number in your chosen unit.
150 gsm
The same cloth in the metric and imperial systems.
- GSM (g/m²)
- 150
- Ounces per sq yard
- 4.42 oz
- Grams per sq yard
- 125.4
GSM measures grams over one square metre while the imperial figure weighs one square yard, so they differ by a fixed factor rather than a scale. Weight guides needle, thread and interlining far more reliably than a fibre name alone, since a heavy cotton and a light linen can ask for opposite settings despite both being plant fibres.
About This Tool
The Fabric Weight calculator converts a cloth weight between the metric GSM system, grams over one square metre, and the imperial ounces-per-square-yard figure, then tells you which broad weight class the number falls into so you can judge what the fabric is suited to.
You type the weight and choose the unit you already have.
It returns both systems plus the grams-per-square-yard intermediate.
The answer ends buying a fabric guessed only by its pretty name.
Weight drives needle size, thread and interlining far more reliably than fibre.
A heavy cotton and a light linen can ask for opposite machine settings.
One shared number lets a metric pattern and an imperial bolt finally agree.
Why Fabric Weight (GSM ↔ oz/yd²) Math Matters
Two fabrics can share a fibre yet behave totally differently at different weights.
GSM is the language of many mill and online shops, oz per yd of others.
Being able to move between them stops you mis-buying from an unfamiliar source.
Weight decides drape, so a lining and a canvas are chosen by GSM first.
Needle and thread gauge should match cloth density, not just its name.
A hem and interfacing fuse differently on a light voile than on a duck canvas.
Reading the class at a glance tells you whether a fabric is a blouse or a coat.
Conversion is exact, so a foreign spec becomes a number you can actually trust.
The Formula
One ounce per square yard equals about thirty four grams per square metre, so a GSM figure is divided by that factor to give ounces, while an ounce figure is multiplied by it to give GSM, and the gram-per-square-yard value follows from the metric area ratio.
- GSM —
- the mass in grams of one square metre of fabric
- oz per yd² —
- the mass in ounces of one square yard of fabric
- Conversion factor —
- the fixed number, near thirty four, linking the two systems
Because the two units weigh differently sized squares, the link between them is a fixed factor rather than a scale, so the same cloth simply reads as a different number in each system.
Worked Example: Step by Step
- 1A shop lists a shirting cotton at one hundred and fifty GSM.
- 2You work in ounces and want to know what that feels like.
- 3Dividing one hundred and fifty by the factor of about thirty four gives the ounce figure.
- 4That comes out near four and a half ounces per square yard.
- 5At that weight the cloth sits squarely in the midweight class.
- 6It is a good shirting or dressweight rather than a coat fabric.
- 7A medium needle and an all-purpose thread suit it well on the machine.
- 8The reverse check, multiplying the ounces back, returns the original GSM number.
- 9So a listing you half understand becomes a weight you can actually plan and sew around.
How to Use This Calculator
- Type in the fabric weight number you already have to hand.
- Select whether that figure is GSM or ounces per square yard.
- Read the matching figure shown in the other unit system.
- Note the broad weight class the calculator assigns it.
- Use that class to guide needle, thread and interfacing choices.
- Convert an unfamiliar foreign spec before you commit to buying.
Key Terms
- GSM
- grams per square metre, the metric measure of fabric weight
- Ounces per square yard
- the imperial measure of how much one square yard of cloth weighs
- Lightweight
- sheer or fine cloth under about one hundred GSM for blouses and linings
- Midweight
- the common dressweight band from roughly one hundred to two hundred GSM
- Heavyweight
- dense cloth over about two hundred GSM for coats, denim and upholstery
- Drape
- how a fabric falls and folds, closely tied to its weight
- Clove weight
- a mill shorthand comparing a hank of yarn to settled fabric grams
- Selvage
- the finished self-edged border of a woven bolt that keeps the weave from unravelling
Fabric Weight (GSM ↔ oz/yd²) Reference Table
| Class | GSM range | Typical use |
|---|---|---|
| Lightweight | under 100 | voile, lining |
| Midweight | 100 to 200 | shirting, dress |
| Heavyweight | over 200 | denim, canvas |
Treat the class bands as rough guides rather than hard borders, since weave changes feel as much as weight does, so a dense midweight twill can hang stiffer than a loose light poplin, and it is always worth ordering a proper swatch to confirm the drape before you commit to a whole costly garment.
Common Mistakes & Pro Tips
- Choosing a fabric by fibre name alone and ignoring the weight that drives drape.
- Assuming a GSM figure means the same as an ounce figure without converting.
- Buying a lightweight cloth for a structured bag that needs real body.
- Using a coarse needle on a fine low-GSM voile and snagging the weave.
- Fusing a heavy interfacing to a light fabric and stiffening it out of shape.
- Confusing grams-per-square-metre with grams-per-square-yard, which differ.
- Trusting a shop photo over the printed weight spec when ordering online.
- Choosing a fabric for a coat at a light weight that simply cannot hold the shape.
- Ignoring that two identical GSM figures can still drape apart on different weaves.
Real-World Use Cases
- Matching a pattern's GSM spec to a US bolt.
- Judging whether a cloth is blouse or coat weight.
- Converting a foreign fabric listing before buying.
- Choosing needle and thread from the fabric weight.
- Picking interfacing weight to suit the base cloth.
- Comparing two fabrics quoted in different units.
- Estimating drape for a flowing skirt panel.
- Deciding if a listed cloth is truly a quilt-weight cotton.
Fabric Weight (GSM ↔ oz/yd²): Frequently Asked Questions
How do I convert GSM to ounces?
Divide the GSM number by about thirty four to get ounces per square yard, since one ounce per yard weighs roughly thirty four grams per metre. The tool does this both ways and shows the exact factor for you.
Is a higher GSM always heavier?
Yes, a larger GSM means more grams over the same square metre, so the cloth is denser and usually stiffer. Weave still matters, but within one fibre the higher number is genuinely the heavier fabric.
Why do shops use two systems?
Metric mills and many overseas sellers quote GSM while US and UK fabric stores often quote ounces per yard. Both describe the same weight, so a clean conversion lets you buy confidently from either source.
What weight is best for clothing?
It depends on the garment, as blouses and linings sit lightweight, shirting and dresses midweight, and coats and denim heavyweight. Match the class to the piece you are making rather than chasing one ideal number.
Does weight change how it sews?
Strongly, since a light low-GSM voile needs a fine needle and gentle tension while a dense canvas wants a heavy needle and longer stitch. Reading the weight first sets your needle, thread and interfacing choices.
This page explains how the fabric weight (gsm ↔ oz/yd²) works, what each input means and where the numbers come from, so you can plan your next make with confidence.
Written by Bobbin & Form Editorial Team
Home sewists & machine-embroidery practitioners
Reviewed by Marie Delacroix
Custom sewist & machine-embroidery technician, 15 years at the machine
Formulas follow standard sewing and needlework references. Results are estimates — always confirm against your pattern and a pre-washed swatch.
Sources & further reading
- Threads Magazine — fabric cutting & yardage guides
- ISO 13934 — textile tensile & fabric property standards
- Your local fabric store's bolt-width charts