Seal-Strength Converter
Convert seal (peel) strength between N/15mm, N/25mm, N/mm, N/m and lbf/inch — so specs and test results line up whatever the width basis.
Inputs
Peel strength is force per unit seal width. Always note the strip width and test standard (e.g. ASTM F88, EN 868) alongside the value.
Result
Values assume the same seal quality — only the width basis or force unit changes. See the seal force calculator and the heat-seal validation guide.
How to use itConvert any seal-strength unit
- Enter the seal (peel) strength value from your test report or specification.
- Select its unit — N/15 mm, N/25 mm, N/mm, N/m, lbf/inch or gf/15 mm.
- Read the equivalents on every common width basis, so you can compare a spec against a test result whatever units each is in.
Why it mattersWhy seal strength needs a width basis
Seal or peel strength is a force per unit width of seal, not a plain force — so a number means nothing without the strip width behind it. European reports usually quote N per 15 mm strip, some use 25 mm, North American ones lbf per inch. "5 N/15mm" and "0.33 N/mm" describe exactly the same seal; quoting one against a spec written in the other is a common source of false pass/fail calls. Normalising to force per millimetre, and back to whatever basis your standard uses, keeps acceptance limits honest.
The mathsThe conversions
1 lbf/inch = 4.448 N ÷ 25.4 mm = 0.175 N/mm
1 gf/mm = 0.00981 N/mm
Everything reduces to force per millimetre of seal width, then scales back up to the basis you need. A 15 mm strip carries fifteen times the per-millimetre force; a 25 mm strip, twenty-five times. Pounds-force per inch converts through 1 lbf = 4.448 N and 1 inch = 25.4 mm. The seal quality is identical across every unit — only the reporting basis differs, which is exactly why the conversion has to be exact.
ReferenceTypical seal-strength ranges
| Application | Typical peel strength |
|---|---|
| Easy-peel lidding (tray, pot) | ~3–8 N/15mm |
| Medical peelable pouch | ~2–5 N/15mm |
| Flexible food pouch (weld seal) | > 20 N/15mm |
| Heavy-duty / retort | > 40 N/15mm |
Good to knowAlways cite the test standard
Alongside the width basis, seal strength depends on the test method — peel angle, jaw speed and sample prep — so cite the standard (ASTM F88 for peel, EN 868 and ISO 11607 for medical) with every value. A peelable medical seal also has to stay within a window: strong enough to hold sterility, weak enough to open cleanly without fibre tear. To design the seal itself, use the seal force calculator; to validate it, see the heat-seal validation guide.
FAQFrequently asked questions
How do I convert seal strength from N/15mm to N/mm?
Divide by 15, because the value is a force spread over a 15 mm wide strip. So 5 N/15mm equals about 0.33 N/mm. To go to a 25 mm basis, multiply the per-mm figure by 25.
Why is seal strength given per unit width?
Because it is a peel force resisted along the width of the seal, not a single point force. Reporting it per millimetre (or per 15 or 25 mm strip) makes results from different strip widths comparable.
How do I convert lbf/inch to N/15mm?
First convert to N/mm: 1 lbf/inch = 4.448 N ÷ 25.4 mm = 0.175 N/mm. Then multiply by 15 for a 15 mm basis, so 1 lbf/inch is about 2.63 N/15mm.
What is a typical seal strength for a peelable pouch?
Easy-peel lidding is usually around 3–8 N/15mm and medical peelable pouches around 2–5 N/15mm — strong enough to hold, weak enough to open cleanly. Permanent weld seals on flexible pouches are much higher, often above 20 N/15mm.
Do I need to state the test standard with a seal-strength value?
Yes. Peel angle, jaw speed and sample width all affect the result, so cite the method — ASTM F88 for peel testing, EN 868 and ISO 11607 for sterile medical packaging — alongside the number and its width basis.