Supported conversions
| Category | Units | Useful for |
|---|---|---|
| Length | in, ft, yd, mm, cm, m | Object dimensions, drops, overlap, hems |
| Area | in², ft², yd², cm², m² | Fabric area and coating coverage |
| Fabric mass | GSM ↔ oz/yd² | Comparing metric and US fabric specifications |
| Sheet thickness | mil ↔ mm | Comparing actual sheet or coating thickness |
Do not convert GSM directly to mil
GSM measures mass per area. Mil measures thickness. A direct conversion would require the material’s density and construction, and even then a woven or coated tarp is not a uniform solid sheet. Use GSM-to-oz/yd² for fabric mass and mil-to-mm for thickness.
1 inch = 25.4 mm; 1 yard = 0.9144 m; 1 avoirdupois ounce = 28.349523125 g; 1 pound = 453.59237 g. The converter rounds only the displayed result.
Source: NIST Unit Conversion and NIST Handbook 44, Appendix C.
Reading a spec sheet that mixes systems
Most confusion happens on listings that quote a metric fabric weight next to imperial dimensions, or that give a thickness where a mass belongs. A few reference points make the numbers legible without a calculator:
| GSM | oz/yd² | Typically |
|---|---|---|
| 90 | 2.7 | Light utility PE, short-term use |
| 150 | 4.4 | Mid-grade PE, general outdoor |
| 250 | 7.4 | Heavy PE / light canvas |
| 450 | 13.3 | Entry PVC-coated polyester |
| 650 | 19.2 | Industrial PVC, transport and equipment |
| 900 | 26.5 | Heavy industrial coated fabric |
The conversion anchor is 1 oz/yd² ≈ 33.906 GSM. If a listing quotes “12 oz canvas,” that is roughly 407 GSM — comparable to entry-level coated fabric by mass, though the two behave very differently in water and abrasion.
Convert once, at the end
Rounding early is the quiet source of errors in tarp math. Converting 14 ft 8 in to 4.47 m, rounding to 4.5, then converting back gives you 14 ft 9.1 in — a 1.1 in drift from one careless step. Over a two-stage conversion on both dimensions, that becomes enough to change which stock size fits.
This converter keeps full precision internally and rounds only what it displays. When you are working by hand, do the same: carry the extra digits, and round once when you write the final number down.
Watch the ounce
Fabric weight uses the avoirdupois ounce, a unit of mass (28.349523125 g). Fluid ounces measure volume and are unrelated. Some listings also quote “ounces per square yard” for a finished tarp rather than the base fabric, which includes coating — check what is being weighed before comparing two products.