OTR / WVTR Converter
Convert oxygen (OTR) and water-vapour (WVTR) transmission rates between per-m², per-100-in² and per-ft² bases — with a barrier-class guide.
Inputs
Always compare barrier values at the same test conditions (temperature and % RH) — the units convert, the conditions do not.
Result
1 m² = 15.5 × 100 in² = 10.764 ft². OTR is normally quoted at 23 °C / 0% RH, WVTR at 38 °C / 90% RH. See the barrier guides in the Knowledge Base.
How to use itConvert barrier units in one screen
- Choose the property — OTR (oxygen, measured in cc) or WVTR (water vapour, measured in grams).
- Enter the transmission rate and its area basis: per m², per 100 in² or per ft² per day.
- Read the equivalents. The tool converts between the metric and imperial area bases and gives a rough barrier-class indication.
Why it mattersWhy barrier units trip people up
Barrier performance decides shelf life, but datasheets quote it inconsistently: European suppliers use cc or grams per square metre per day, North American ones per 100 square inches or per square foot. A film listed at "0.6 cc/100in²/day" and one at "9.3 cc/m²/day" are identical — but only after conversion. Comparing quotes, matching a spec, or checking a laminate meets an oxygen limit all depend on getting the area basis right, and the factor of about 15.5 between per-m² and per-100-in² is easy to drop.
The mathsThe conversions
Rate per m² = rate per 100 in² × 15.5 = rate per ft² × 10.764
Transmission rate scales with area, so a larger reference area carries a larger number for the same film. Converting per-100-in² to per-m² multiplies by 15.5; converting per-ft² to per-m² multiplies by 10.764. The physical property is unchanged — only the area basis differs. Critically, the units convert but the test conditions do not: an OTR measured at 23 °C and 0% RH cannot be compared with one at 50% RH, and WVTR is condition-sensitive too.
ReferenceTypical barrier levels (per m²/day)
| Barrier class | OTR (cc/m²/day) | WVTR (g/m²/day) |
|---|---|---|
| Ultra-high (EVOH, metallised, foil) | < 1 | < 1 |
| High | 1–10 | 1–5 |
| Medium (PET, PA) | 10–100 | 5–20 |
| Low (PE, PP) | > 100 | > 5 |
Good to knowAlways state the test conditions
Because oxygen and moisture transmission depend strongly on temperature and humidity, a barrier figure is meaningless without its conditions. Quote OTR at its standard 23 °C / 0% RH (or note the RH used) and WVTR at 38 °C / 90% RH, and never compare two films measured differently. For matching a barrier to a product, see the material guides in the Knowledge Base.
FAQFrequently asked questions
How do I convert OTR from per 100 square inches to per square metre?
Multiply by 15.5, because one square metre equals 15.5 times 100 square inches (1550 in²). So 0.6 cc/100in²/day is about 9.3 cc/m²/day. WVTR converts the same way.
What is the difference between OTR and WVTR?
OTR (oxygen transmission rate) measures how much oxygen passes through a film, in cc per area per day. WVTR (water vapour transmission rate) measures moisture, in grams per area per day. Both describe barrier performance but for different permeants.
What counts as a high-barrier film?
As a guide, an OTR below about 1 cc/m²/day and a WVTR below about 1 g/m²/day are high-barrier, typical of EVOH, metallised or foil structures. PET and PA are medium barrier; PE and PP are low barrier.
Why must I state the test conditions with a barrier value?
Because oxygen and moisture transmission change sharply with temperature and humidity. OTR is normally quoted at 23 °C / 0% RH and WVTR at 38 °C / 90% RH. Two films are only comparable if measured under the same conditions.
Does this converter change the barrier value or just the units?
Only the units. It re-expresses the same transmission rate on a different area basis (per m², per 100 in² or per ft²). The underlying barrier property, and its test conditions, are unchanged.