How do you calculate screen efficiency?

Divide the undersize that correctly reported to the unders by the total undersize present in the feed, then multiply by 100. With 210 kg passed of 250 kg present, screen efficiency is 84%.

What is a good screen efficiency for a disc screen?

Well-maintained disc and trommel screens commonly run 85-95% efficiency on undersize. The 84% here is just under a 90% target, a 6-point gap that typically points to disc wear, wrapping or excessive burden depth.

What does the gap to target tell me?

It is your efficiency minus the target. Here 84% minus 90% is a 6-point shortfall, meaning the screen is letting roughly 40 kg of undersize per 250 kg of feed carry over instead of dropping through.

Why is my screen efficiency dropping over time?

Common causes are worn or wrapped discs, screen blinding, too-fast belt speed, or burden depth too high to let fines reach the screen surface. Each lowers the share of undersize that makes it to the unders.

Does screen efficiency account for oversize ending up in the unders?

No. This metric only tracks how much undersize is recovered. Oversize misplaced into the unders is a separate purity issue; measure it independently and weigh both when tuning.

How do I improve screen efficiency?

Restore correct disc spacing, clean wrapping, reduce burden depth so fines reach the screen, and slow the belt if material passes too quickly. Closing the 6-point gap to 90% means recovering more of that 40 kg carryover.

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Screen Efficiency Calculator

Screen efficiency measures how well a disc screen, trommel or vibrating screen separates undersize material from the feed, expressed as the percent of available undersize that actually reports to the unders. MRF process engineers and maintenance teams use it to tune disc spacing, belt speed and screen angle, and to know when worn discs or wrapping are degrading separation. It matters because poor screening sends fines into the wrong stream, increases contamination downstream and overloads optical sorters. Tracking efficiency against a target shows whether a screen is doing its job or quietly failing.

What this calculator does

Estimate the screening efficiency of a trommel, disc, or ballistic screen and see how far it sits from the design target.
Use it after a composition study on screen overs and unders to decide whether the screen needs cleaning, deck replacement, or feed rate trimming.
It computes screen efficiency as undersize correctly passed divided by total undersize in the feed, and the point gap to your target.

Formula used

Screen efficiency = undersize correctly passed / total undersize in feed x 100
Gap to target screen efficiency = screen efficiency - target screen efficiency

Inputs explained

Undersize correctly passed to unders:
Total undersize present in feed:
Target screen efficiency:

How to use the result

Use it after a screen rebuild, during a wrapping or fines-carryover investigation, or in routine process audits.
It only measures recovery of undersize to unders; it does not capture misplaced oversize in the unders, so pair it with a misplacement check for a full picture.

Current U.S. benchmarks

Steel mill PPI stands at 348.53 (BLS, May 2026), up 6.7% from a year earlier. New factory orders are up 2.3% year over year (Census).

Common questions

How do you calculate screen efficiency? Divide the undersize that correctly reported to the unders by the total undersize present in the feed, then multiply by 100. With 210 kg passed of 250 kg present, screen efficiency is 84%.
What is a good screen efficiency for a disc screen? Well-maintained disc and trommel screens commonly run 85-95% efficiency on undersize. The 84% here is just under a 90% target, a 6-point gap that typically points to disc wear, wrapping or excessive burden depth.
What does the gap to target tell me? It is your efficiency minus the target. Here 84% minus 90% is a 6-point shortfall, meaning the screen is letting roughly 40 kg of undersize per 250 kg of feed carry over instead of dropping through.
Why is my screen efficiency dropping over time? Common causes are worn or wrapped discs, screen blinding, too-fast belt speed, or burden depth too high to let fines reach the screen surface. Each lowers the share of undersize that makes it to the unders.
Does screen efficiency account for oversize ending up in the unders? No. This metric only tracks how much undersize is recovered. Oversize misplaced into the unders is a separate purity issue; measure it independently and weigh both when tuning.

Last reviewed 2026-05-12.