Injection Molding Tolerance Calculator
DIN 16742 / ISO 20457 tolerance groups & US per-material tolerances
Plastic tolerances are size- AND resin-driven — with honest confidence marks so approximations are never dressed up as exact.
Nominal size + tolerance group
Full TG table (±mm, by size)
About the Injection Molding Tolerance Calculator
Tolerancing an injection-moulded plastic part is a different game from machining. This tool covers the two paradigms in one place — the European/international DIN 16742 / ISO 20457 tolerance-group system, and the US per-material commercial/precision guide — and marks every cell with its confidence so approximations are never dressed up as exact.
The one thing to understand: DIN 16742 and ISO 20457 are the same source
These are not two rival systems. The German DIN 16742:2013 and the international ISO 20457:2018 share the same tolerance-group (TG1–TG9) structure and are identical cell-for-cell up to 400 mm (verified against three independent sources). They only diverge above 400 mm — for example TG6 at 400–500 mm is ±1.60 mm under DIN 16742 but ±1.25 mm under ISO 20457. Underneath, the TG groups are built on the ISO 286 basic tolerance grades (IT), the same backbone the machining world uses. The genuinely different paradigm is the American per-material approach, where tolerance depends on the resin rather than a size-indexed table.
Two things that trip people up
Tool-related (W) vs non-tool-related (NW). Unlike ISO 286, a plastic tolerance depends on whether the dimension sits inside one mould half (W, tighter) or spans the parting line / is affected by slides and ejector pins (NW, looser). General untoleranced dimensions always use the NW column. Material dependence. Injection tolerance is driven by resin shrinkage — POM shrinks around 2% while PC shrinks around 0.6%, so the same nominal size is far harder to hold in POM. Check the shrinkage of your resin on the Injection Molding Parameters page.
How to use
- TG groups: enter a nominal size, pick a tolerance group (TG6 is the common default) and choose W or NW to read the ± tolerance from DIN 16742 / ISO 20457.
- US per-material: pick a resin and dimension for the commercial or precision ± tolerance from the industry molding guide.
- Standards & material dependence: see the TG↔IT map, the DIN/ISO divergence and how shrinkage sets what is achievable.
Frequently Asked Questions
Q: Is DIN 16742 the same as ISO 20457?
Almost. They share the TG1–TG9 structure and are identical cell-for-cell up to 400 mm. They diverge only above 400 mm (e.g. TG6 W at 400–500 mm is ±1.60 mm in DIN 16742 vs ±1.25 mm in ISO 20457). For the vast majority of parts, which are under 400 mm, the two give the same numbers.
Q: What is the difference between W and NW tolerances?
W (tool-related) applies to dimensions formed within a single mould half and is tighter. NW (non-tool-related) applies to dimensions across the parting line or affected by moving mould parts (slides, ejectors) and is looser. The rule is NW at a given band equals W at the next-larger band. General/untoleranced dimensions always use NW.
Q: Why does the same tolerance group give different values at different sizes?
Because, like ISO 286 IT grades, DIN 16742 tolerance groups are size-dependent — a TG6 tolerance grows with the nominal dimension. In fact each TG maps to an ISO 286 IT grade (TG6 ≈ IT13–IT14 depending on the size band), so it inherits the same size dependence.
Q: Are the US per-material tolerances an official standard?
No. They come from the US industry molding-tolerance guide (commercial/precision, descending from SPI/DME molder practice), not a national standard like DIN 16742. Achievable tolerance depends heavily on part design, tooling and process control, so treat them as a starting point and negotiate with your supplier.
Last updated: July 2026 | Reference tool for planning. Verify critical callouts against the current standard (DIN 16742:2013, ISO 20457:2018).
