Fabric GSM Calculator: Sample Weight to g/m² and oz/yd²

How to use

Fabric GSM calculation rests on two measurements: the weight of a sample and its area. Use the tool in this order:

1. Choose the calculation. “From a sample” finds g/m² from a weighing; “Convert” converts between g/m² and oz/yd².
2. Choose the sample shape. A GSM cutter is a round sample cutter with an area of 100 cm² (1/100 m²); if you use one, keep the default shape. Without a cutter, enter the sides of a rectangle (cm), the diameter of a circle (cm) or the area itself (cm²).
3. Enter the weight in grams. You can enter up to five samples cut from different places of the fabric; the tool shows the mean, the lowest and highest value, the standard deviation and the coefficient of variation.
4. Add the fabric width (optional). If you enter the width in cm or inches, the tool also gives the weight per linear meter (g/m), the meters per kilogram and the ounces per linear yard.

Use a period as the decimal separator (1.84). The result updates as you type; with JavaScript turned off, press “Calculate”. The “Calculation steps” section shows how the tool read the number you entered.

Formula

GSM is the mass of a sample divided by its area. Because the area is measured in cm², the result is multiplied by 10,000 (1 m² = 10,000 cm²):

g/m² = sample weight (g) × 10,000 ÷ sample area (cm²)

The sample area depends on the shape:

• GSM cutter (round): 100 cm² (fixed)
• Rectangle: side a × side b
• Circle: π × diameter² ÷ 4
• Free area: the cm² value you enter

If you enter several samples, each is calculated separately and the result is the mean. The sample standard deviation is s = √(Σ(xᵢ − x̄)² ÷ (n − 1)) and the coefficient of variation is CV (%) = s ÷ x̄ × 100. If CV exceeds 5%, the tool suggests cutting new samples from other places of the fabric, away from the selvage.

Unit conversions:

• oz/yd²: 1 oz/yd² = 28.3495 g ÷ (0.9144 m)² ≈ 33.906 g/m² (exact value 33.9057…; NIST SP 811). So oz/yd² = g/m² ÷ 33.906 and g/m² = oz/yd² × 33.906.
• Linear weight (g/m): g/m² × fabric width (m). A width in cm is converted to meters with 0.01, a width in inches with 0.0254.
• Meters per kilogram (m/kg): 1,000 ÷ (g/m).
• Ounces per linear yard: g/m × 0.9144 ÷ 28.3495.

Worked example

Start with the values the tool opens with: a sample cut with a 100 cm² GSM cutter that weighs 3 g.

1. Area: 100 cm² (GSM cutter).
2. GSM: 3 × 10,000 ÷ 100 = 300 g/m².
3. oz/yd²: 300 ÷ 33.906 ≈ 8.85 oz/yd².

Without a cutter the logic is the same. A 20 × 25 cm rectangle is 500 cm²; if it weighs 9.5 g, the fabric is 9.5 × 10,000 ÷ 500 = 190 g/m². A circle 11.28 cm in diameter has an area of about 100 cm² (99.93 cm²); a 3 g sample then gives 300.2 g/m².

Weigh three samples (GSM cutter; 1.80 g, 1.84 g and 1.78 g) and you get 180, 184 and 178 g/m². The mean is 180.7 g/m², the standard deviation 3.06 and the coefficient of variation 1.7%, so the samples agree well.

With a fabric width of 180 cm and a GSM of 240 g/m², the linear weight is 240 × 1.80 = 432 g/m. That means 1,000 ÷ 432 ≈ 2.315 m/kg: 1 kg of this fabric is about 2.31 m long. 432 g/m is also about 13.93 oz per linear yard. To go from kilograms to meters or back, use the fabric meter to kg calculator.

GSM to oz/yd² and oz/yd² to GSM conversion tables

The tables below are calculated with the constant the tool uses (1 oz/yd² = 33.9057… g/m²). In denim, weight is usually given in oz/yd²: Cotton Incorporated writes that finished denims range from 3.5 to 16.5 oz/yd² (CottonWorks). For example, 8 oz/yd² is about 271.2 g/m².

g/m² to oz/yd²

oz/yd² to g/m²

Common mistakes

• Entering the decimal separator wrongly. On this English page, a comma followed by exactly three digits counts as a thousands separator: “1,800” is read as 1800. Use a period for 1.8 g and check the value the tool read in the calculation steps.
• A balance that is not precise enough. A 100 cm² sample of a 160 g/m² fabric weighs only 1.6 g, so a kitchen scale that reads to 1 g is not enough. Use a balance that reads to at least 0.01 g, or take a larger sample: a 50 × 50 cm sample is 0.25 m². The tool warns when the area is below 50 cm².
• Relying on one sample. Several samples cut from different places, away from the selvage, show the spread; Online Clothing Study recommends five.
• Not stating the condition of measurement. When a knitted fabric relaxes, the loops move closer together and GSM rises. In Cotton Incorporated's measurement, a 28-gauge single jersey weighed 135 g/m² as it came off the machine and 176 g/m² fully relaxed (about 30% more; ISP 1009, 2004). For more detail, see fabric weight (GSM).
• Confusing oz with oz/yd². For fabric, “oz” means oz/yd². “Oz per linear yard” is weight per length and cannot be converted to g/m² without the fabric width.

Standards and measurement: how is fabric weight measured?

Mass per unit area is measured by a standard, and the right one depends on the fabric type:

Conditioning the sample in the ISO 139 standard atmosphere (20 °C, 65% relative humidity) before weighing reduces the effect of moisture on the weighing.

The tool is exact as far as the formula goes; the uncertainty of the result comes from the input: balance, cut size, moisture and the condition in which the fabric was measured. Our recommendation is to write GSM into a contract not as a single figure but with a target value, a tolerance and the condition of measurement. For an official result or a dispute, turn to a test laboratory.

Which GSM suits which product is covered in the T-shirt, hoodie and jogger GSM guide. If you are sourcing fabric in Turkey, see the knitted fabric and woven fabric suppliers.