GSM and oz/yd² tell you how much tarp material weighs per unit area. Mil and mm tell you how thick it is. Use the correct conversion, compare the construction, and turn a supplier’s headline number into a specification you can approve.
For importers, fabricators, fleets and OEM buyers, DERFLEX can review PVC coated fabric and custom tarp requirements around material weight, reinforcement, finishing and the intended application.
Finished tarp performance includes the fabric, seams, hems and attachment points. An ounce rating describes only one part of that system.
The direct answer
What do GSM, oz and mil mean on a tarp?
GSM and oz/yd² measure mass per area; mil measures thickness. Convert GSM to oz/yd² by dividing by 33.905747. Convert mil to mm by multiplying by 0.0254. There is no universal GSM-to-mil or oz-to-mil conversion for a woven, coated tarp.
GSM
Grams per square meter
The mass of one square meter of material, normally stated for the finished coated fabric. It does not include a complete tarp’s hardware or packing.
oz/yd²
Ounces per square yard
The same area-weight property in imperial units. An “18 oz tarp” needs confirmation that the unit really means oz/yd².
mil
One thousandth of an inch
A thickness unit: 1 mil = 0.001 inch. Higher mil means a thicker measurement, without identifying the yarn, coating or test performance.
mm
Millimeters of thickness
The metric thickness unit. A 0.50 mm measurement is approximately 19.69 mil. Mil and millimeter are different units.
Also keep yarn size, weave count and reinforcement separate from area weight. The tarp specification glossary explains the related terms used in supplier quotations.
Work with your own numbers
Tarp unit converters.
Two independent tools keep area weight and thickness on their correct scales. Results are mathematical conversions, not a product recommendation.
01 / AREA WEIGHT
GSM ↔ oz/yd²
19.17 oz/yd²650 GSM ÷ 33.905747
GSM = oz/yd² × 33.905747
02 / THICKNESS
mil ↔ mm
0.508 mm20 mil × 0.0254
mm = mil × 0.0254
Keep both results independent. Entering 650 GSM does not determine the mil thickness. Entering 20 mil does not determine the GSM. Ask for the measured thickness and area weight of the actual material.
03 / MATERIAL MASS
How much will the fabric weigh?
Estimate a rectangular, single-layer panel. This excludes hems, overlap, extra reinforcement, hardware and packaging.
39.00 kg / 85.98 lb60.00 m² × 650 GSM ÷ 1,000 · material only
Two scales, shown separately
Tarp GSM, ounce and mil conversion charts.
Use the left chart for area weight and the right chart for thickness. Rows across the two charts are not equivalent product grades.
Thickness values are exact unit conversions. They do not specify waterproofing, tear strength, UV durability or the fabric’s area weight.
Conversion reference: NIST Special Publication 811, Appendix B. The tools use 28.349523125 g per avoirdupois ounce and 0.9144 m per yard to calculate the area-weight factor.
Worked example / Area weight
What does an 18 oz tarp weigh?
18 oz/yd² ≈ 610.3 GSM
A 10 m² single-layer panel has a theoretical fabric mass of approximately 6.103 kg. This number says nothing about its exact mil thickness. For commercial ounce classes, see the vinyl tarp weight chart.
Worked example / Thickness
Is 20 mil the same as 20 oz?
20 mil = 0.508 mm
20 oz/yd² is approximately 678.1 GSM. A product may happen to have both specifications, but neither value proves the other. Obtain both measurements for the particular construction being quoted.
Read the construction behind the number
Why can’t GSM be converted directly to mil?
A coated tarp is a composite, not a uniform solid sheet. The yarns, weave, coating on each face, formulation and surface finish all contribute differently to its mass and measured thickness.
Two materials can therefore share one GSM target but differ in thickness, bending behavior or mechanical performance. A density-based estimate for a uniform film should not be transferred to a woven PVC coated fabric.
For PVC coated polyester tarpaulin, request the finished material’s area weight and thickness together with reinforcement details and comparable test results.
Top coatingPVC formulation, coating build and surface finish
Woven reinforcementYarn size, weave and warp / weft construction
Back coatingCoating build, adhesion and fabrication surface
Conceptual structure only; layers are not drawn to scale. Confirm the actual coating or lamination construction on the approved sample.
Choose for the job
Which tarp specification should you compare?
Start with the material family and the failure you need to prevent. Area weight is useful within a comparable construction; it cannot rank every tarp material on one durability scale.
Material family / What to request from a supplier
Material
Useful headline units
Compare alongside the units
Procurement question
PE / woven poly tarp
GSM or oz/yd², finished thickness in mil or mm
Woven core, lamination, UV formulation, edge reinforcement and dimensions
Are thickness and weight measured on finished material under an agreed sampling method?
PVC / vinyl coated polyester
GSM or oz/yd² plus mil or mm where required
Base fabric, coating adhesion, tensile / tear results, welds and cold flexibility
Does the quoted construction address wear, handling and attachment loads?
Canvas / treated textile
GSM or oz/yd²
Dry or treated weight basis, treatment, moisture behavior and dimensional stability
Does the ounce rating include the treatment applied to the cloth?
Mesh tarp
GSM or oz/yd² plus opening / coverage specification
Open area, yarn construction, tear performance and finished edge design
Is airflow or containment the objective, and what opening size is needed?
Clear flexible PVC sheet
Mil or mm, with area weight if needed
Film formulation, reinforcement if present, flexibility, clarity and seams
Are you comparing unreinforced film with a scrim-reinforced product?
A practical PVC tarp starting point
The following bands are illustrative procurement discussion ranges within PVC coated polyester. They are not standardized duty classes or confirmed stock specifications.
Starting area-weight band
Discussion direction
Key check
300–450 GSM
Lighter covers with frequent handling
Required tear / tensile performance and exposure
550–650 GSM
Reusable general or equipment covers
Coating adhesion, seams and handling mass
750–900 GSM
Higher-wear or repeated-use covers
Abrasion evidence, cold flex and attachment design
Above 900 GSM
Projects where additional material mass is justified
Actual failure mode and safe handling arrangements
What actually changes the decision?
Frequent folding: evaluate flexibility and fold durability at the service temperature.
Rubbing on edges: evaluate local protection and abrasion performance, not just extra GSM.
Wind and tie-down loads: review tensile / tear data, hems, reinforcement and attachment layout.
Long outdoor exposure: request the UV / weathering requirement and relevant evidence.
Water exclusion: inspect coating continuity and seam quality; neither GSM nor mil proves waterproofing.
An approved sample and agreed acceptance criteria should settle the selection. For a broader application overview, visit the DERFLEX industrial and custom tarp range.
Material structureReview the coated fabric surface and base-fabric construction. A photograph does not establish GSM or thickness.Roll-goods sourcingSpecify roll width, length, area weight, color and fabrication requirements as separate order details.Finished cover performanceSeams and attachment points matter alongside the fabric specification in transport applications.
Before approving a bulk order
Verify the sample. Then agree the tolerance.
A nominal specification is a target. Approval needs a defined measurement method, sampling locations and acceptance criteria.
01
Measure area weight on a known area
Use a suitably accurate balance and a measured coupon, away from hems, seams and hardware. GSM = sample mass in grams ÷ sample area in m². For example, 6.50 g from a 100 cm² coupon equals 650 GSM. Check multiple locations using agreed conditioning and sampling procedures.
02
Measure thickness under agreed conditions
Use a suitable thickness gauge, with contact pressure, foot size and sampling positions agreed in advance. Avoid seam stacks and folded edges when checking the base material. Record the readings and method rather than relying on a single maximum.
03
Separate fabric mass from shipment mass
Length × width × GSM estimates the single-layer fabric mass. Seam overlaps, welded hems, wear pads, webbing, D-rings and eyelets add mass. Roll cores, protective wrapping and pallets belong in shipping weight, not fabric GSM.
04
Agree each acceptance criterion
State whether the requirement applies to an average, minimum or individual reading. Define allowable variation for GSM, thickness, width, length and color separately. A mathematical conversion adds precision to the unit, not to the manufacturing tolerance.
05
Compare strength using the same method
Request test method, units and warp / weft results for tensile and tear strength. Also review coating adhesion and finished seam or attachment performance where they affect the application. Numbers measured under different procedures may not be comparable.
06
Link the order to an approved construction
Keep the sample reference, agreed data sheet, finishing drawing and acceptance criteria with the order. DERFLEX’s quality control process covers material weight, thickness, mechanical checks and batch inspection; request the documentation needed for your project.
Avoid the ounce-unit trap. 1 oz/ft² equals 9 oz/yd², or approximately 305.15 GSM. “Oz per linear yard” additionally depends on fabric width. Write the complete area unit in every specification and supplier comparison.
Move from a number to a quotable specification
Build a clearer tarp RFQ.
Use this worksheet to prepare your specification. Copy the summary into DERFLEX’s quote form or send it with your drawing and technical requirements.
Include what the fabric must do.
For PVC tarp roll goods, custom covers, bulk sourcing and OEM programs, weight is only the starting point. Tell DERFLEX the service conditions and finished construction you need.
Application and the main wear or failure concern
Finished size, drops, overlap or roll width / length
Area weight with a complete unit; thickness if required
Yarn / weave direction and mechanical targets
UV, temperature, flame or other test requirements
Welds, hems, reinforcement and hardware layout
Quantity, destination and required delivery date
Confirm before placing the order: material construction, approved sample, dimensional basis, tolerances, MOQ, lead time and packing. These depend on the agreed project; no fixed value is assumed here.
Short answers for comparing data sheets, discussing samples and preparing an order.
How do I convert tarp GSM to oz/yd²?
Divide GSM by 33.905747. For example, 650 GSM is approximately 19.17 oz/yd². For the reverse conversion, multiply oz/yd² by 33.905747. Confirm the ounce rating is per square yard, not per square foot or per linear yard.
How many mil is an 18 oz tarp?
There is no universal answer. An 18 oz/yd² tarp converts to about 610.3 GSM, but its thickness must be measured or supplied on the product data sheet. Base fabric, coating ratio, material density and surface texture affect thickness.
What is 20 mil in millimeters?
20 mil equals 0.508 mm, or 508 micrometers. Multiply mil by 0.0254 to get millimeters. A mil is one thousandth of an inch; it is not a millimeter.
Is a higher GSM tarp always stronger?
No. Higher GSM means more material mass per square meter. Compare reinforcement, tensile and tear results in both directions, coating adhesion, seams and attachment design. Additional coating mass does not automatically create stronger yarns or tie-down points.
What GSM should I specify for a heavy-duty PVC tarp?
Use the application to define a starting point, then approve a tested construction. In this guide, 550–650 GSM is an illustrative band for reusable general covers and 750–900 GSM for higher-wear covers. These are procurement discussion bands, not universal performance classes or a guarantee of suitability.
How do I calculate the weight of a tarp?
For a rectangular single-layer panel, material mass in kilograms equals length in meters × width in meters × GSM ÷ 1000. A 6 m × 10 m panel at 650 GSM has a theoretical material mass of 39 kg. Hems, seams, reinforcement, hardware, packaging and dimensional tolerances change the actual finished or shipping weight.
Does GSM or mil prove that a tarp is waterproof?
No. Neither unit proves waterproof performance. Review the coating or film continuity, pinholes, seams, joining process and the required water-resistance test. Mesh and breathable fabrics need a different evaluation even when their area weight is high.
What information does DERFLEX need for a tarp quotation?
Provide the application, material family, finished dimensions or roll requirements, GSM or oz/yd², measured thickness if required, quantity and destination. Add exposure conditions, reinforcement, eyelet or D-ring layout, seam details and any required test criteria. Ask DERFLEX to confirm the sample, tolerance, MOQ, lead time and packing for the agreed construction.
Need help matching weight to the application?
Send the dimensions, exposure and construction requirements for a specification review.
