Draft Angle Calculator for injection molding.
Calculate optimal draft angles from material type, surface texture standard (VDI, SPI, MT), and part depth. The most comprehensive draft angle tool available, built by injection molding engineers.
Draft Angle Calculator
Texture requires additional draft: the tool adds 1° per 0.025 mm (0.001 in) of texture depth. Core-side walls get +0.5° because parts shrink onto cores as they cool.
Draft angle reference charts.
Industry-standard guidelines by material and texture. Filter and search 100+ materials and 60 texture grades across VDI, SPI, Mold-Tech, Yick Sang, and Charmilles standards.
Draft Angle by Material Type
| Material | Abbreviation | Min Draft | Recommended | Max Draft | Notes |
|---|
Additional Draft for Surface Texture
| Standard | Class/Grade | Depth (mm) | Depth (in) | Additional Draft | Description |
|---|
Industry rule of thumb: add 1° of draft per 0.025 mm (0.001 in) of texture depth.
Why draft angle matters.
Plastic shrinks 0.4% to 3% as it cools, pulling away from cavity surfaces while gripping cores, ribs, and bosses. Without enough draft, ejection forces climb: bent ejector pins, drag lines, cosmetic defects, and longer cycles.
Cavity Side (External)
Parts shrink away from cavity surfaces during cooling. Standard draft angles of 0.5 to 1 degree are usually sufficient for smooth release.
Core Side (Internal)
Parts shrink onto core features, gripping them tightly. Add 0.5 to 1 degree of additional draft for internal walls and ribs.
Textured Surfaces
Surface texture creates mechanical interlocking. Add approximately 1 degree per 0.025 mm of texture depth to overcome it.
Deep Draws
Deep walls accumulate more surface contact. Consider 1.5 to 2 degrees minimum for draws over 100 mm.
Material matters: low-friction resins like Nylon (PA) and Acetal (POM) can release with 0.25° to 0.5°, while flexible TPE and TPU grip mold surfaces and typically need 2° or more. Glass-filled compounds are abrasive and should always carry 1.5° minimum. High-shrinkage materials (PP at 1.5 to 2.5%) grip cores harder than low-shrinkage ones (PC at 0.5 to 0.7%); estimate your material with the plastic shrinkage calculator.
For complex geometry: ribs need 0.5° to 1° per side, bosses need draft on both walls, and shut-off surfaces must keep consistent draft or they flash. A 50 mm deep feature at 1° draft loses roughly 1.75 mm of wall thickness from bottom to top. Our plastic part design and Moldflow analysis services de-risk these details before steel is cut.
Draft angle questions, answered.
What is the minimum draft angle for injection molding?
The absolute minimum depends on material type, surface finish, and part depth. For polished surfaces, 0.25 to 0.5 degrees is possible with low-friction materials like Nylon or Acetal. For most applications with ABS, PC, or PP, plan for 0.5 degrees minimum and 1 degree recommended. Textured surfaces require additional draft, typically 1 degree per 0.025 mm of texture depth. Use the calculator above to dial in your exact combination of material and texture.
How do I calculate draft angle for textured parts?
The standard formula is: Total Draft = Base Draft + (Texture Depth / 0.025 mm). For example, a VDI 30 texture (0.050 mm depth) on ABS would require 1.0 degree base draft plus 2.0 degrees texture draft, for 3.0 degrees total. The calculator applies this automatically for VDI, SPI, and Mold-Tech standards. Always verify your part geometry can accommodate the required draft before specifying aggressive textures.
Why is more draft needed on core side features?
During cooling, plastic shrinks away from cavity (external) surfaces but shrinks onto core (internal) surfaces. That shrinkage creates significant gripping force on cores, ribs, and bosses, and the longer the cooling time, the tighter the grip. Adding 0.5 to 1.0 degree of extra draft on core side features compensates for the effect. Deep internal features over 50 mm deserve even more, especially with high-shrinkage materials like PP.
Can I injection mold a part with zero draft?
It is possible but comes with real trade-offs: longer cycle times, higher ejection forces, potential cosmetic defects, accelerated mold wear, and risk of part damage. Zero draft is typically only justified for short features under 10 mm with low-friction materials and polished surfaces. Even 0.25 degrees dramatically improves ejection reliability. If your design truly requires zero draft, have an injection molding consultant evaluate feasibility first.
How does draft angle affect part wall thickness?
Draft creates a tapered wall that varies in thickness from top to bottom. For every 25 mm of depth, 1 degree of draft adds approximately 0.44 mm of thickness change. That affects part strength, cooling rate, and surface appearance. Specify nominal wall at the mid-point of the draft, and account for the variation in your thickness analysis. Moldflow simulation will flag any fill or cooling issues the taper introduces.
More free calculators on the engineering tools page. Need a DFM review on a real part? Ask an engineer.
Need expert help with
your mold design?
MoldMinds provides injection molding consulting, DFM review, and tooling project management. Let 15+ years of experience help you get it right the first time.