Suit Fabric Weight Explained: Ounces, Grams and Seasons

Every fabric book lists a weight next to each swatch, and it is the single best clue to when a suit can be worn. It is also one of the most confusing numbers in tailoring. English books quote ounces, Italian books quote grams, some online shops quote grams per square meter, and few of them say which is which. Here is how suit fabric weight is measured, how to convert it, which weight suits which season and city, and what weight does to drape, creasing and durability.

How is suit fabric weight measured?

Suit fabric weight is the weight of one running length of fabric at its full woven width. English mills and merchants quote ounces per running yard; Italian mills quote grams per running meter. A running yard or meter is measured along the length of the roll, and suiting is usually woven about 150 cm (58 to 60 in) wide. So a 10 oz fabric means one yard of it, about 150 cm across, weighs 10 oz.

This is different from how denim, knits and many other fabrics are sold. Those are usually quoted per square yard or per square meter, written as gsm (grams per square meter). Because suiting is about 1.5 meters wide, one running meter covers about 1.5 square meters. The same suiting fabric therefore has a gsm figure about a third lower than its grams per meter. Online shops do not always say which unit they use, so always check.

How do you convert ounces to grams for suit fabric?

One ounce is 28.35 g and one yard is 0.914 m, so 1 oz per running yard equals about 31 g per running meter. That gives four quick rules for a fabric about 150 cm wide.

• Ounces to grams per meter: multiply by 31. A 10 oz fabric is about 310 g.
• Grams per meter to ounces: divide by 31. A 280 g fabric is about 9 oz.
• Grams per meter to gsm: divide by 1.5. A 300 g fabric is about 200 gsm.
• Gsm to grams per meter: multiply by 1.5. A 200 gsm fabric is about 300 g per meter, or about 9.7 oz.

Why do fabric books give ranges like 9/10 oz?

Many books quote a weight as a pair, such as 9/10 oz or 280/310 g. It means the fabric sits between the two figures. Weight can vary slightly from piece to piece and between finishes, so mills give a band rather than promise a single number. Treat 9/10 oz as about 9.5 oz (295 g).

What is a good weight for a suit?

For most people, the best single weight is about 10 oz (310 g), in the middle of the year-round band of 9 to 11 oz (280 to 340 g). It is heavy enough to drape cleanly and shed creases, and light enough for heated and air-conditioned offices. Lighter fabrics are for heat; heavier ones are for cold weather and a fuller, more structured look. The full reasoning is in our guide to year-round suit fabric.

What weight suit for summer?

Choose 7 to 9 oz (220 to 280 g) for a summer suit. Below about 7 oz (220 g), fabrics become fragile, crease easily and show every bulge. Open weaves break the rule that lighter is cooler: a high-twist plain weave at 9 to 10 oz (280 to 310 g) can feel cooler than a dense 8 oz (250 g) worsted, because air passes straight through it. See high-twist wool and fresco and the best suit fabric for hot weather.

What weight suit for winter?

For a winter suit, choose about 12 to 14 oz (370 to 430 g). Flannel usually sits here, and it is the classic cold-weather suit fabric; see flannel suits. Tweeds often run heavier, from about 14 oz (430 g). Remember that most winter days are spent indoors. In a heated office, a 10 to 11 oz (310 to 340 g) worsted under a good overcoat is often more comfortable than a heavy suit, and our guide to overcoat styles covers the coat.

Which suit weight is best for your city?

Climate moves the bands by an ounce or two. These picks assume most of the working day is spent indoors.

How does fabric weight affect drape, creasing and durability?

Weight changes how a suit behaves, not only how warm it is. A heavier fabric hangs under its own weight, so the trousers fall straight, the jacket skims the body and small creases pull out as you move. It hides the outline of a phone or wallet, holds the shape a tailor presses into it and stands up to friction at the seat and elbows. A lighter fabric is cooler and more comfortable in heat. It also creases more readily, shows what is in your pockets, moves in the wind and wears through sooner where it rubs.

Why vintage suits feel so heavy

Suits used to be much heavier. In 1938 the King ordered 15 to 16 oz (465 to 495 g) milled worsteds from a Huddersfield mill, and even Fresco, now a summer fabric, was woven at about 11 to 18 oz (341 to 558 g) in 1950. As homes, offices and cars became heated and air-conditioned, the everyday suit moved toward 10 oz (310 g). If you buy a vintage suit, expect it to be warmer and to drape more heavily than a modern one.

Should trousers be heavier than the jacket?

In a suit, both are cut from the same fabric, so the question is which weight serves both. Trousers do the hard work: they bend at the knee, rub at the thighs and take your weight at the seat, so they wear out first and benefit from a little more weight. For odd trousers, about 10 to 13 oz (310 to 400 g) hangs well and lasts. If you choose a light fabric for a suit, order a second pair of trousers at the same time; see how to care for a suit.

How do you choose a fabric weight at a tailor?

Weight is the one number in a fabric book that tells you when you will wear the suit. Learn the 31 g rule, check the unit and read weight together with the weave. For the other numbers on the label, see Super numbers explained, and for a walk through a whole fabric book, see how to read a fabric bunch.

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