GSM, Denier and Mesh in PP Woven Fabric
The formula linking mesh, denier and GSM in PP woven fabric, with worked examples for bag weight and roll length, and why GSM alone is not strength.
Three numbers describe a woven polypropylene fabric: mesh, denier and GSM. Quotes usually show only the last one, which is the easiest to measure and the easiest to misread. Two fabrics at the same GSM can be built from different tapes on a different weave and behave differently on a filling line. This guide gives the arithmetic that ties the three together, so a buyer can check a quote, convert a roll into bags, and see what a change of one number does to the other two.
What each number measures
- Mesh
- Tapes per inch, written warp x weft. A 10 x 10 fabric has ten tapes per inch along the roll and ten across it.
- Denier
- Weight in grams of 9,000 metres of one tape. A 900 denier tape weighs 0.1 gram per metre.
- GSM
- Grams per square metre of finished fabric. It is the result of mesh and denier.
The formula
When warp and weft tapes share one denier, fabric weight is: GSM = (warp mesh + weft mesh) x denier / 228.6. The constant is not arbitrary. One inch is 1/39.37 of a metre, so a square metre holds mesh x 39.37 tapes in each direction, each one metre long, and each metre of tape weighs denier / 9,000 grams. Dividing 9,000 by 39.37 gives 228.6. When the two directions use different tapes, weigh them separately: GSM = (warp mesh x warp denier + weft mesh x weft denier) / 228.6. Weaving bends the tapes slightly around each other, so a loom-state fabric lands a few percent above the calculated figure.
| Mesh (warp x weft) | 700 denier | 900 denier | 1,100 denier |
|---|---|---|---|
| 10 x 10 | 61 GSM | 79 GSM | 96 GSM |
| 12 x 12 | 73 GSM | 94 GSM | 115 GSM |
| 14 x 14 | 86 GSM | 110 GSM | 135 GSM |
Same GSM, different fabric
A 12 x 12 fabric in 800 denier tape and an 8 x 8 fabric in 1,200 denier tape both calculate to 84 GSM. They are not interchangeable. The first has more, lighter tapes: a closer surface that holds fine powder better and takes print more evenly. The second has fewer, heavier tapes: wider gaps at the crossings, more sifting with a fine product, and a different tear path when a hook or a forklift tine catches it. A purchase order that states GSM alone lets either one be delivered. Stating mesh and denier, or mesh and GSM, removes the ambiguity. Our standard PP woven fabric roll is specified both ways: 60-120 GSM in tapes of 500-1,500 denier.
Where tape denier comes from
Denier is set on the tape line by the width and thickness of the slit tape: denier = width in millimetres x thickness in microns x polymer density x 9. A tape 2.5 mm wide and 40 microns thick in polypropylene of density 0.91 comes to 2.5 x 40 x 0.91 x 9 = 819 denier. Density is where a quote can mislead. Calcium carbonate filler is denser than polypropylene, so a heavily filled tape reaches a target denier, and therefore a target GSM, with less polymer in it. The fabric weighs what the order says and carries less load. Ask for tensile strength as well as GSM.
Lamination adds to GSM, it does not change the weave
A coated fabric is quoted as one total: base fabric plus coating. A 90 GSM laminated fabric with a 20 GSM coating is a 70 GSM weave underneath, and it is the weave that carries the load. Our PP laminated woven fabric roll runs 80-130 GSM in total with 15-30 GSM of that as PP coating, so when comparing a laminated quote with an unlaminated one, subtract the coating before comparing strength. The coating is there for the moisture barrier and the print face, which the comparison of coating types in our lamination guide covers in detail.
From GSM to bag weight
Circular looms produce a tube, so a bag has two faces of fabric. Bag weight in grams = 2 x lay-flat width in metres x cut length in metres x GSM. Cut length is the finished length plus the bottom fold and any top hem. A 50 x 80 cm sack cut at 86 cm from 100 GSM fabric weighs 2 x 0.50 x 0.86 x 100 = 86 grams before sewing thread. That figure is the check to run when bags arrive: weigh ten, average them, and compare with the number the specification implies. Our PP woven cement bag is specified at 90-115 GSM in 45 x 75 cm and 50 x 80 cm, which puts an honest bag in a narrow, predictable weight band.
From GSM to metres per kilogram
Rolls are sold by weight and converted by length, so the useful conversion is metres per kilogram. For tubular fabric: metres per kg = 1,000 / (2 x lay-flat width in metres x GSM). A 60 cm tube at 70 GSM gives 1,000 / (2 x 0.60 x 70) = 11.9 metres per kilogram, so one tonne converts to about 11,900 metres, or roughly 13,800 bags at an 86 cm cut. For fabric slit open and supplied flat, drop the factor of two. Running this before ordering shows how many bags a minimum order quantity really is: five tonnes of that fabric is close to 69,000 sacks.
What to write on the order
| State this | It prevents |
|---|---|
| Mesh, warp x weft | A coarse weave in heavy tape substituted for a close weave |
| GSM with a tolerance | Argument at receiving over what counts as underweight |
| Coating GSM, stated separately | A thick coating over a light weave passing as a heavy fabric |
| Tensile strength, warp and weft | Filler making up the weight while strength falls |
| Lay-flat width and roll length | Shortfall in the number of bags a roll yields |
The published ranges show how far these numbers move from one fabric to the next. Our anti-slip PP woven fabric runs 70-130 GSM, the printed PP woven fabric roll 80-110 GSM with 15-25 GSM of that as coating, and the UV stabilized PP woven fabric 80-150 GSM for outdoor use. Each range is a different combination of mesh and denier chosen for the job, which is the reason a GSM figure means little without the other two.
Frequently asked questions
How do I measure GSM without a laboratory?
Cut a square of exactly 10 x 10 cm from a single layer, weigh it on a scale that reads to 0.01 gram, and multiply by 100. Take five squares from different places across the width and average them, because weight varies slightly from edge to centre.
Is a higher GSM always stronger?
No. GSM is weight. Strength depends on how well the tapes were stretched during extrusion and on how much of the weight is polymer rather than filler. Two fabrics of equal GSM can differ widely in breaking load, which is why tensile strength belongs on the specification.
What does 10 x 10 mesh mean?
Ten warp tapes and ten weft tapes in each inch of fabric. It says how closely the fabric is woven and nothing about how heavy each tape is.
Does the formula work for laminated fabric?
It gives the weight of the weave only. Add the coating weight to reach the total GSM of a laminated fabric, and compare strength on the weave figure.
Why is my measured GSM a little above the calculated value?
Tapes follow a slightly wavy path over and under each other, so a square metre contains a little more than a metre of tape per end. Expect a few percent on a plain weave.