Fabric Weight Guide — GSM to Oz Conversion

Fabric Weight Categories

Fabric weight determines drape, durability, warmth, and suitable uses. Here is how fabric weights are categorized in both systems:

Category	oz/yd²	GSM	Common Uses
Lightweight	1 – 5 oz	30 – 170 GSM	Shirting, blouses, light dresses, scarves, lining
Medium	5 – 8 oz	170 – 270 GSM	Quilting cotton, dresses, sheets, lightweight pants
Medium-Heavy	8 – 12 oz	270 – 400 GSM	Denim, upholstery, canvas, heavy trousers, bags
Heavy	12 – 16 oz	400 – 550 GSM	Outerwear, winter coats, upholstery, workwear
Very Heavy	16+ oz	550+ GSM	Rugs, industrial fabric, heavy canvas, bag fabric

Conversion Formula

oz to GSM: GSM = oz × 33.906
GSM to oz: oz = GSM ÷ 33.906

The conversion factor 33.906 comes from the relationship between grams per square meter and ounces per square yard. One ounce equals 28.3495 grams, and one square yard equals 0.836127 square meters. So 1 oz/yd² = 28.3495 ÷ 0.836127 = 33.906 GSM.

Quick Reference Conversions

GSM	oz/yd²	Category
50	1.5 oz	Lightweight
100	2.9 oz	Lightweight
150	4.4 oz	Lightweight
200	5.9 oz	Medium
250	7.4 oz	Medium
300	8.8 oz	Medium-Heavy
350	10.3 oz	Medium-Heavy
400	11.8 oz	Medium-Heavy
450	13.3 oz	Heavy
500	14.7 oz	Heavy
600	17.7 oz	Very Heavy

Fabric Weight by Project

Choosing the right fabric weight is critical for project success. Here is what weight works for common sewing projects:

Curtains & Drapery

Medium-weight fabric (5–8 oz / 170–270 GSM) is best for most curtains. It drapes well without being too stiff. Sheer curtains use lightweight fabric (1–3 oz / 30–100 GSM). Blackout curtains use medium-heavy fabric (8–10 oz / 270–340 GSM) with a coating.

Upholstery

Upholstery requires medium-heavy to heavy fabric (8–14 oz / 270–475 GSM). This weight provides the durability needed for daily use. Lightweight fabrics wear through quickly on furniture. Commercial upholstery is typically 12+ oz / 400+ GSM.

Dresses & Apparel

Dress weight depends on the style. Summer dresses and blouses use lightweight fabric (3–5 oz / 100–170 GSM). Structured dresses and sheaths use medium weight (5–7 oz / 170–240 GSM). Evening gowns may use anything from lightweight silks to medium-weight brocades.

Quilts

Quilting cotton is typically medium weight (4–6 oz / 135–200 GSM). This weight is sturdy enough to hold piecing stitches while remaining soft enough to quilt by hand or machine. Backing fabric should be similar weight to prevent distortion.

Winter Coats & Outerwear

Winter coats need heavy fabric (12–16 oz / 400–550 GSM). Wool coating, heavy tweed, and quilted outerwear fabrics fall in this range. They provide warmth, structure, and wind resistance. Lighter fabrics won't hold the shape of a coat.

Pants & Trousers

Pants need medium to medium-heavy fabric (7–10 oz / 240–340 GSM). Lightweight fabrics wrinkle easily and don't drape well for trousers. Denim jeans typically use 10–14 oz / 340–475 GSM fabric. Stretch denim is often lighter due to elastane content.

Bags & Accessories

Tote bags, backpacks, and accessories need medium-heavy to heavy fabric (10–14 oz / 340–475 GSM). Canvas, twill, and heavy upholstery fabrics work well. Lighter fabrics won't hold their shape or carry weight.

How Fabric Weight Is Measured

Fabric weight is measured using two main systems:

GSM (Grams Per Square Meter)

GSM is the metric standard for fabric weight. A 1m × 1m sample of fabric is weighed in grams. Higher GSM means heavier, denser fabric. GSM is used worldwide and is the standard measurement for most fabric manufacturers.

oz/yd² (Ounces Per Square Yard)

oz/yd² is the imperial system used primarily in the United States. A 36" × 36" sample of fabric is weighed in ounces. Most U.S. fabric stores list weight in oz/yd² for upholstery, denim, and canvas fabrics.

Note: Fabric weight is different from thread count or fabric density. Two fabrics with the same weight can have very different feels depending on fiber type and weave structure. For example, 200 GSM linen feels much different from 200 GSM cotton sateen.

Frequently Asked Questions

What is GSM in fabric?

GSM stands for Grams Per Square Meter. It is the standard metric measurement for fabric weight. A higher GSM means heavier, thicker, and usually more durable fabric. Most fabric manufacturers list GSM on their specifications.

How do I measure fabric weight at home?

Cut a 10cm × 10cm sample (4" × 4"), weigh it on a precision scale, then multiply by 100 for GSM. For oz/yd², cut a 36" × 36" sample and weigh it in ounces. Most home sewers rely on the manufacturer's listed weight instead.

What fabric weight is best for curtains?

Medium-weight fabric (5–8 oz / 170–270 GSM) is ideal for most curtains. It drapes well and provides good light filtering. Sheer curtains use lightweight fabric (1–3 oz). Blackout curtains need medium-heavy fabric (8–10 oz) with a special coating or lining.

What fabric weight is best for upholstery?

Upholstery requires medium-heavy to heavy fabric (8–14 oz / 270–475 GSM). Residential upholstery typically uses 8–12 oz fabric. Commercial upholstery requires 12+ oz for durability. Lightweight fabric will wear through quickly on furniture.

What's the difference between GSM and oz?

Both measure the same thing — fabric weight — but in different units. GSM (grams per square meter) is the metric standard. oz/yd² (ounces per square yard) is the imperial standard used in the US. To convert: divide GSM by 33.906 to get oz, or multiply oz by 33.906 to get GSM.

What is the most common fabric weight for quilting?

Quilting cotton is typically 4–6 oz (135–200 GSM). This medium weight is sturdy enough to hold piecing stitches and quilting, while remaining soft enough to manipulate. Most quilt shops sell 100% cotton in this weight range.

Does higher GSM mean better quality fabric?

Not necessarily. Higher GSM means heavier fabric, but quality depends on fiber type, weave, and finishing. A 300 GSM polyester may be lower quality than a 150 GSM linen. Choose fabric weight based on your project needs, not as a quality indicator.

Once you know your fabric weight, use the yardage calculator to determine how much fabric you need. The fabric cost calculator can help you budget based on weight and price per yard.