Tolerances & Standards

Understanding achievable tolerances is essential for designing injection molded parts that are functional without over-specifying (which adds cost). This guide covers standard tolerance grades and practical guidelines.

Standard Tolerance Grades

The international standard for injection molded part tolerances is ISO 20457 (replacing DIN 16901). Tolerances are specified by grade and material group:

Dimension (mm)	Fine Grade (mm)	Standard Grade (mm)	Coarse Grade (mm)
0-10	±0.08	±0.15	±0.25
10-30	±0.12	±0.20	±0.35
30-100	±0.20	±0.35	±0.55
100-300	±0.35	±0.55	±0.80
300-500	±0.55	±0.80	±1.20

Material Group Effects

• Group 1: PE, PP, PS — moderate shrinkage, tightest tolerances achievable
• Group 2: ABS, PA, PC, POM — moderate-high shrinkage
• Group 3: PBT, PET, PPS — high shrinkage, wider tolerances needed
• Group 4: Liquid crystal polymers, reinforced materials — anisotropic shrinkage

Critical Tolerance Features

Some features inherently require wider tolerances:

• Across parting line: ±0.25mm minimum due to mold mismatch
• Moving core features: ±0.15mm for sliding actions
• Draft-affected dimensions: Vary with draft angle and depth
• Weld line areas: May show local deviation