Sample weight calculator: from a weighed swatch to g/m² (ISO 3801)

Finds a fabric’s actual weight from the mass and size of the swatch you cut — valid for every fabric type, including woven, weft knit and warp knit.

Formula

Fabric weight (g/m²) = sample mass (g) × 10,000 ÷ (length (cm) × width (cm)). The constant 10,000 is the cm²→m² conversion (1 m² = 10,000 cm²). Imperial equivalent: oz/yd² = g/m² ÷ 33.906.

Worked example

A 10 × 10 cm swatch weighs 1.8 g → area = 10 × 10 = 100 cm². Fabric weight = 1.8 × 10,000 ÷ 100 = 180 g/m². Imperial equivalent = 180 ÷ 33.906 = 5.31 oz/yd². Cutting 20 × 20 cm from the same fabric would give 7.2 g and still return 180 g/m² — sample size does not change the result, only its precision.

Frequently asked questions

Why weigh instead of calculating from construction?

Estimating weight from construction is technology-specific: weaving needs thread density and crimp, weft knitting needs loop length, and warp knitting (raschel, tricot) needs the run-in per guide bar. Some of those are MACHINE parameters — a buyer holding the fabric cannot know them. Weighing makes no construction assumption at all: it works the same way for every fabric type, even nonwovens, and the result is a measurement rather than an estimate.

How large should the sample be?

A larger sample is more precise, because cutting tolerance and balance error stay small relative to the total. A 100 cm² circular cutter is common for ISO 3801; measuring by hand, 10 × 10 cm is a practical baseline. Cut clean edges, flatten creases, and take the sample from the body of the fabric rather than the selvedge; sampling several points and averaging also reveals within-lot variation.

Should the sample be conditioned?

For a figure you intend to declare, yes. Textile fibres take up moisture from the air and the balance weighs that moisture too; the standard atmosphere is 20 °C and 65% relative humidity. Polyester has very low regain (0.4%), so the deviation is small, but it becomes significant in cotton blends. To convert to commercial (conditioned) weight, use the conditioned weight calculator.

My measured value differs from the quoted weight — why?

Three usual causes: whether the fabric is greige or finished (finishing, compacting and heat-setting all raise weight), whether the sample was damp or dry, and within-lot tolerance. Catalogue weights are given as typical bands; the acceptance tolerance is stated per order in your quotation. If you have measured a difference, share your sample size and weighing conditions and we will verify it together.