PVC tarpaulin weight and thickness describe two different measurements. GSM and oz/yd² express mass per area; millimetres and mil express thickness. You can convert within each pair, but a weight figure cannot be converted into one universal thickness for every PVC-coated construction.
For procurement and quality teams, the useful next step is to make the quotation, sample measurements and acceptance specification use the same units and conditions. This guide covers those calculations and measurement checks.
Read the unit before comparing two quotations
| Label | Quantity described | Detail that prevents a misleading comparison |
|---|---|---|
| GSM or g/m² | Mass per unit area | State whether it covers the complete coated material |
| oz/yd² | Mass per unit area in customary units | Write the area unit; “oz” alone is incomplete |
| mm | Thickness | Identify whether it is total material thickness or a layer measurement |
| mil | Thickness in thousandths of an inch | Keep it distinct from millimetres |
| kg per roll | Total mass for a roll | Separate fabric from core and packaging; include usable width and length |
For a reinforced tarp material, the purchasing weight normally needs to identify the complete composite. A base-fabric-only value and a finished coated-material value should not be compared as if they describe the same sample.
Convert GSM and ounces per square yard
The NIST conversion table gives 1 oz/yd² as approximately 33.90575 g/m². Multiply oz/yd² by 33.90575 to obtain GSM, or divide GSM by 33.90575 for oz/yd².
| GSM | Approximate oz/yd² |
|---|---|
| 300 | 8.85 |
| 400 | 11.80 |
| 500 | 14.75 |
| 600 | 17.70 |
| 650 | 19.17 |
| 700 | 20.65 |
| 900 | 26.54 |
An 18 oz/yd² specification is approximately 610.30 g/m². A 600 GSM specification is approximately 17.70 oz/yd². If a supplier calls 600 GSM “18 oz” as a rounded trade description, agree which numerical requirement controls the order rather than treating both as exact equivalents.
Convert mil and millimetres without mixing them with weight
For thickness, 1 mil = 0.001 inch = 0.0254 mm. Multiply mil by 0.0254 for millimetres; divide millimetres by 0.0254 for mil.
| Thickness in mil | Thickness in mm |
|---|---|
| 10 | 0.254 |
| 15 | 0.381 |
| 20 | 0.508 |
| 30 | 0.762 |
| 40 | 1.016 |
For example, 20 mil equals 0.508 mm. That calculation does not supply a GSM value. Reinforcement, PVC formulation, layer proportions and surface texture can change how total thickness relates to material mass.
Ask for measured finished thickness when thickness is part of acceptance. A general “600 GSM = X mil” table is not reliable across different coated fabrics.
Check sample mass per area with a known specimen size
The basic calculation is specimen mass in grams divided by specimen area in square metres. For an illustrative 10 cm × 10 cm specimen, the area is 0.01 m²; a measured mass of 6.00 g gives 600 g/m².
The specimen needs an accurately known area and a mass reading appropriate to its size. Include the full material construction being evaluated, and keep moisture and conditioning consistent with the agreed method. Do not use a hemmed piece, a seam overlap or a printed label as if it were an unprocessed sample of the roll.
One piece demonstrates the calculation, not the uniformity of an entire batch. For acceptance, agree specimen locations, number of readings, conditioning, reporting and permitted variation with the supplier or testing laboratory.
Make thickness readings comparable
Record the instrument, contact conditions, specimen conditioning and measured locations used for a thickness result. A flexible or embossed material may give different readings when contact pressure or position changes, so two unqualified thickness figures are not necessarily comparable.
Distinguish total composite thickness from the thickness of one PVC layer. On a textured material, also state how the surface profile is handled by the agreed method. Report the individual readings or the agreed summary rather than assuming that every point equals the nominal label.
Reconcile roll mass with the acceptance specification
A material-only estimate follows: usable width × length × GSM ÷ 1,000 = kilograms. A nominal 2 m × 50 m roll at 600 GSM contains a calculated 60 kg of fabric. Core, wrapping and other packaging add mass and should be listed separately when using a shipment weight.
Finish the comparison with a written target, unit, tolerance, measurement method and sampling plan for each acceptance item. Differences between a rounded product name and a measured result should be assessed against that agreement, not an assumed industry-wide tolerance.
If you now need to decide which construction and weight suit the application, continue with the tarpaulin GSM buying guide. That decision requires use conditions and performance evidence in addition to the unit calculations.
