Snap-Fit Calculator

Instant Strain & Safety Factor Estimates

Enter your feature dimensions and material properties to predict:

  • Maximum root strain (cantilever)
  • Hoop strain (annular)
  • Safety factor vs yield
  • Automatic PASS / FAIL recommendations

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Instantly Validate Your Cantilever & Annular Snap-Fit Designs

Designing plastic snap fits shouldn’t feel like guesswork. A snap can “fail” in different ways—it might break, or it might yield and permanently deform, leaving a loose, unreliable joint. Our Snap-Fit Calculator provides a fast, engineering-backed way to estimate whether your snap feature is likely to remain elastic, take a permanent set, or risk fracture during assembly.

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Predict Failure Before You Cut Tools

Avoid costly iterations by simulating strain levels in both cantilever and annular (continuous ring) snap-fit geometries. Enter your dimensions and material/properties, and the calculator returns a clear result based on classical mechanical design approximations.

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Built for Real Design Scenarios

Manufacturers and engineers often rely on rough intuition for snap fits—until something breaks. This calculator delivers quantitative strain results using proven analytical methods, helping you design with confidence.

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Fast, Clear Results

Just enter your key dimensions and material strain limit. The calculator shows:

  • Maximum root
    strain (cantilever)
  • Hoop strain (annular)
  • Safety factor
  • Automatic PASS/
    FAIL result
  • Engineering notes
    explaining the assumptions

What the snap-fit calculator covers and how it works

Cantilever snap fits

Uses a classical cantilever approximation to estimate maximum strain at the root during snap deflection. Ideal for enclosure latches, battery doors, consumer electronics, clips, and tabs. Also reports a rough force estimate (linear elastic) for quick assembly feel checks.

Cantilever snap fit diagram

Cantilever snap dimensional inputs

Annular snap fits

Uses a thin-ring/diametric interference approximation to estimate hoop strain for snap-on caps, lids, collars, and cylindrical assemblies such as packaging caps, medical device housings, threadless closures, and push-on features. Includes optional inputs (thickness, engagement width, and friction) to provide a simplified estimate of insertion force.

Note:This annular model assumes a continuous ring, not a segmented arc.

Annular snap fit diagram

Annular snap dimensional inputs

Material selection with auto-filled properties

Choose a common plastic to auto-fill:

Modulus (E)
Yield strength (σy)
Optional fracture strain (εf) (editable)

From these, the calculator estimates yield strain (εy ≈ σy/E) and applies a Safety Factor vs Yield (FoS) to set a conservative allowable strain.

Clear results you can act on

For each snap type, the calculator reports:

  • Calculated strain (cantilever root strain or annular hoop strain)
  • Yield strain and allowable strain (based on FoS)
  • Optional fracture-likely flag (if εf is provided)
  • A clear outcome:
  • Elastic (PASS) — full recovery expected
  • Permanent set likely (FAIL) — may deform and lose retention
  • Fracture likely (FAIL) — cracking/breakage risk elevated
No spreadsheets, no hand calculations—just fast, transparent guidance.

Snap Fit Calculator Assumptions & limitations

Snap fits are sensitive to real-world effects—temperature, creep, moisture (nylon), molding orientation, stress concentrators, and part-to-part variation. This calculator is intended for early-stage feasibility and design guidance. For critical designs or high-cycle snaps, validate with testing and/or FEA.

Download the snap-fit calculator today

and make it snappy!