How many parts fit on a standard sprue?

A typical injection moulded sprue for 1:35 scale holds 20-40 parts depending on part size. Smaller scales (1:72) can fit more parts per sprue. The sprue frame is usually 150-200 mm on each side.

What determines parts per sprue?

Part size, gate positions, runner layout and mould cavity space. Larger parts need more space and may have only 10-15 per sprue. Small detail parts can have 40+ per sprue. Draft angles and ejection also affect layout.

What is runner waste?

Runner waste is the plastic in the sprue frame and gates that connects parts but gets discarded. Typically 15-25% of total plastic in a kit is runner material. Some manufacturers use thinner runners to reduce waste.

How does scale affect sprue layout?

Larger scales mean bigger parts, so fewer fit per sprue. A 1:16 kit may need 8-10 sprues for the same subject that fits on 3-4 sprues at 1:72. Larger parts also need thicker runners for proper plastic flow.

ModelCalcs

Sprue Layout Calculator \u2014 Parts Per Sprue Planning

Calculate number of sprues and parts per sprue for a given total parts count.

Total Parts

Total number of parts in the kit

Parts Per Sprue

Max parts on each sprue

Kit Scale

Model scale affects part size

Sprue Type

Runner layout style

How We Calculate This

This calculator divides your total parts count into sprues, estimates the runner material needed and calculates the waste percentage.

How it works

Parts are divided evenly across sprues up to your parts-per-sprue limit. Runner length is estimated from gate widths and runner widths scaled for your kit scale. Waste is calculated as the ratio of runner material to total plastic volume.

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Always verify quantities before purchasing materials.