Updated: 2026-05-29Tool: Online calculatorStatus: editorially reviewed May 2026Editorial: KunststoffWissen
Formula · m = mass · V = volume · ρ = density
m [g] = V [cm³] × ρ [g/cm³]
Basic definition density = mass / volume. Volume per geometry: cuboid a·b·c, cylinder π/4·d²·h, sphere π/6·d³, hollow cylinder π/4·(D²−d²)·h.
Online calculator
Note: Based on solid density at 23 °C. Real moulded parts deviate due to shrinkage, voids and fillers. For filled compounds use the datasheet density. All information without warranty.
What the part weight is used for
The weight of a plastic part is the basis for material demand, shipping weight and cost estimation. It follows from the simplest relation in physics: mass = volume × density. Given the part volume and the material density, the weight is found in one step.
The calculator above takes the volume either from a chosen base geometry (cuboid, cylinder, sphere, hollow cylinder) or directly as a number and multiplies it by the material density. Handy wherever no CAD volume exists yet or a quick estimate is enough.
Volume from geometry
For the common solids the elementary volume formulas apply:
Cuboid: V = a · b · c
Cylinder: V = π/4 · d² · h
Sphere: V = π/6 · d³
Hollow cylinder (tube/bushing): V = π/4 · (D² − d²) · h
Complex parts can often be approximated as one or more of these solids. For exact figures any CAD system gives the precise volume – then use the "custom volume" input in the calculator.
Worked example
A POM cuboid 50 × 30 × 20 mm (density 1.41 g/cm³):
V = 5.0 · 3.0 · 2.0 = 30 cm³, m = 30 × 1.41 = 42.3 g.
The same volume in PP (0.905 g/cm³) weighs only 27.2 g – the material accounts for over 55 % weight difference at equal size. This is exactly why lightweighting looks at density first: switching from POM to a lighter polymer or a foamed part noticeably cuts weight and material cost.
Choosing the right density
Use the solid density at 23 °C, not the bulk density of the pellets. Guide values: PP 0.905 · PE-HD 0.95 · PS/ABS 1.05 · PA66 1.14 · PC 1.20 · PET 1.38 · POM 1.41 g/cm³. Two practical points:
Fillers raise density: glass or mineral add 0.1–0.3 g/cm³ – for filled compounds use the datasheet value.
Foams and voids lower it: real moulded parts can deviate slightly through shrinkage and entrapped air.
The calculation is based on solid density; real parts deviate through shrinkage, voids and fillers. For the shot weight (part plus runner, times cavity count) use the shot-weight calculator, for material cost per part the unit-cost calculator. Current material prices are in the polymer-price ticker.
FAQ
How do I calculate the weight of a plastic part?
Weight = volume × density. Volume comes from the geometry (e.g. cuboid a·b·c or cylinder π/4·Ø²·height), density from the material (e.g. PP 0.905 g/cm³). Example: a PP cuboid 50×30×20 mm = 30 cm³ × 0.905 = 27.2 g. For complex parts read the volume from the CAD model and enter it under "Custom volume".
What densities do common plastics have?
Guide values (g/cm³): PP 0.905, PE-LD 0.92, PE-HD 0.95, PS 1.05, ABS 1.05, PMMA 1.18, PA6 1.13, PA66 1.14, PC 1.20, PET 1.38, POM 1.41, PVC 1.38, PTFE 2.16. Glass-fibre reinforcement raises density (PA66-GF30 ≈ 1.36). The solid density is what matters, not the pellet bulk density.
How do I enter a complex part volume?
Choose "Custom volume (cm³)" and enter the volume in Dimension 1. Any CAD program provides the volume (mass properties) — often even the weight directly if density is set in the material. This calculator is meant for quick estimates without CAD.
Why does the calculated weight differ from the real part?
Moulded parts are slightly smaller than nominal volume due to shrinkage, may contain voids or foam structure, and can include fillers of different density. For precise values weigh the real part or use the datasheet density of the specific compound.
Sources & method: Basic definition of density; volume formulas of elementary geometry. Material densities from datasheets (23 °C).