The standard (formerly DIN 16742) defines the manufacturing tolerances and acceptance conditions for plastic molded parts . It is primarily used to align expectations between designers and manufacturers regarding dimensional accuracy in injection molding and other plastic processes. Key Tolerance Group: TG6
The standard uses two main tables to determine the applicable tolerance: INTERNATIONAL STANDARD ISO 20457
Because ISO 20457 is a copyrighted document published by the International Organization for Standardization, the full PDF cannot be downloaded for free. It must be purchased from an authorized standards distributor. However, accessing the tolerance tables and the document itself is straightforward.
which includes the first few pages and Table 8 (General Tolerances). Detailed Overviews
ISO 20457 has become the global benchmark for tolerancing injection-molded plastic parts. By adopting this standard, designers and engineers can move away from guesswork and ambiguous specifications. iso 20457 tolerance table pdf
It reduces disputes between part designers and molders by setting clear boundaries. Factors Influencing Plastic Tolerances
A universal language between designers and molders worldwide.
Reserved for optimized, premium engineering plastics molded under tightly regulated laboratory or high-end cleanroom conditions. Tooling costs are exceptionally high.
Using the "Medium" class for a 45mm part, the linear tolerance is ± 0.8 mm. This means your part can be 44.2 mm to 45.8 mm. The standard (formerly DIN 16742) defines the manufacturing
Download our free ISO 20457-compliant tolerance table template (PDF) — fill in your material and process class to generate custom tolerances. (Link placeholder)
In North America, the SPI tolerance system—using letter-number grades such as A1 (commercial) through B3 (fine)—remains common. SPI tolerances are expressed as a base tolerance plus an increment per inch of dimension. A B1 tolerance on a 2-inch PP dimension yields approximately ±0.010 inches (0.254 mm). Many Chinese manufacturers familiar with European standards can map SPI specifications to ISO 20457 grades. To avoid misunderstandings when sourcing from offshore suppliers, specify ISO 20457 TG grades directly rather than relying on SPI conversion.
While ISO 20457 is specifically designed for plastic molded parts, ISO 2768 specifies general tolerances for machined metal components. ISO 2768 is typically applied to mold base plates, ejector pins, and other steel components machined via CNC, not to the plastic parts themselves.
ISO 20457 specifies the possible manufacturing tolerances for plastic molded parts. It applies to injection molding, compression molding, transfer molding, and rotational molding of thermoplastic and thermosetting materials. The standard serves three primary functions: It must be purchased from an authorized standards
Concise recommendation
(e.g., ABS, PC) have low, uniform shrinkage.
Read the corresponding plus/minus ( ±plus or minus ) value in millimeters. Simplified ISO 20457 Tolerance Lookup