Enter Dimensions
Example Data Table
| Scenario | Mode | Original | Final | Stretch Ratio | Percent Change |
|---|---|---|---|---|---|
| Film draw (machine direction) | Length | L₀ = 100 mm | L = 250 mm | 2.5000 | 150.0000% |
| Sheet area change | Area | 200×100 mm | 240×95 mm | 1.1400 | 14.0000% |
| Foam block expansion | Volume | 50×30×10 mm | 65×32×12 mm | 1.6640 | 66.4000% |
| Fiber stretching | Length | L₀ = 80 mm | L = 120 mm | 1.5000 | 50.0000% |
| Coating spread | Area | 150×60 mm | 170×58 mm | 1.0956 | 9.5589% |
Numbers above are illustrative. Your values can differ by material and process settings.
Formula Used
Stretch ratio is the final size divided by the original size. It is dimensionless and often written as λ.
- Length stretch:
λ = L / L₀ - Area stretch:
λA = A / A₀, whereA = L×W - Volume stretch:
λV = V / V₀, whereV = L×W×T - Engineering strain:
ε = (L − L₀) / L₀(or areal/volumetric equivalents) - True strain:
εt = ln(λ)(uses the natural logarithm)
√λA or ∛λV.
How to Use This Calculator
- Select the calculation type: Length, Area, or Volume.
- Choose a unit and keep it consistent for all inputs.
- Enter original dimensions (L₀, W₀, T₀) and final dimensions (L, W, T).
- Press Calculate to show results above the form.
- Use the CSV or PDF buttons to export the latest results.
Practical Notes
- If λ > 1, the part stretched; if λ < 1, it contracted.
- In many polymer processes, “draw ratio” is the same as length stretch ratio.
- True strain is helpful when stretches are large and cumulative.
- If your inputs are noisy, increase rounding or measure again.
Stretch Ratio Guide
1) Why Stretch Ratio Matters
Stretch ratio (λ) summarizes how much a part elongates. For example, λ = 2.50 means the final dimension is 2.5× the original, equal to 150% elongation. Teams track λ to relate speed, temperature, and tension with thickness and strength. It also supports process documentation needs.
2) Length Stretch in Film and Fiber Lines
In machine-direction drawing, length stretch is the primary metric. If L₀ = 100 mm and L = 250 mm, λ = 2.50 and true strain is ln(2.50) ≈ 0.916. Fiber lines may use λ ≈ 2 to 8, depending on grade.
3) Area Stretch for Sheet Forming
When both length and width change, area stretch is more descriptive. If a sheet goes from 200×100 mm to 240×95 mm, the area ratio is λA = 1.14, meaning a 14% area increase. The equivalent linear ratio √λA ≈ 1.068 simplifies comparisons.
4) Volume Stretch in Foams and Expansion
For expansion or compression, volumetric ratio provides the clearest view. A block changing from 50×30×10 mm to 65×32×12 mm has λV = 1.664, or 66.4% volume growth. The cube-root equivalent ∛λV ≈ 1.185 estimates an average per-axis change.
5) Engineering vs True Strain
Engineering strain uses ΔL/L₀ and is simple for modest changes. True strain uses ln(λ) and adds cleanly across stretching steps. Two sequential stretches of λ = 1.5 and λ = 1.6 give ln(1.5)+ln(1.6)=ln(2.4), matching an overall λ of 2.4.
6) Typical Target Ranges
Targets vary by material and product. Packaging films often run λ ≈ 1.2 to 4.0, while specialty oriented films can exceed λ ≈ 6.0. Biaxial lines may specify MD and TD ratios plus λA; for instance MD = 3.0 and TD = 3.5 implies λA ≈ 10.5. Confirm limits with supplier data.
7) Measurement and Data Quality
Measure dimensions at consistent locations and temperatures. Use at least 5 samples per batch, then report the mean and range of λ. A tight process might hold λ within ±0.03 for critical products. Use calibrated calipers, a ruler jig, or image measurement. If drift appears, verify roller speed ratio and nip pressure.
8) Quality Control and Reporting
Combine stretch ratio with thickness, density, or weight data to spot root causes. A rising λ with falling thickness can indicate overheating or excessive draw tension. Use CSV export for quick SPC work, and PDF export for audit-ready summaries with inputs and mode.
FAQs
1) What is stretch ratio?
Stretch ratio (λ) is the final dimension divided by the original dimension. It is dimensionless and indicates elongation when λ > 1, or contraction when λ < 1.
2) Is draw ratio the same as stretch ratio?
In many polymer and film lines, draw ratio refers to the same length-based ratio, λ = L/L₀. Some plants also use separate ratios for different directions, such as MD and TD.
3) Can stretch ratio be less than 1?
Yes. If the final dimension is smaller than the original, λ < 1. This represents shrinkage, compression, or relaxation, and the percent change will be negative.
4) Why does the calculator show true strain?
True strain uses ln(λ) and is useful for large stretches and multi-step processes. It adds directly across steps, which can be more consistent than engineering strain for big deformations.
5) Do units affect stretch ratio?
No. Because λ is a ratio, any consistent unit cancels out. Still, selecting the correct unit improves readability in reports and helps avoid data-entry mistakes.
6) How do I handle biaxial stretching?
Use Area mode by entering original and final length and width. The calculator reports λA and √λA, letting you compare a biaxial change to an equivalent single-direction ratio.
7) How do I export my results?
After you calculate, use the CSV or PDF buttons in the Results panel. The export includes inputs, outputs, and the selected mode, making it easy to share or archive.