Ask what a shaker screen removes and you will get two different kinds of answer: a mesh count like ‘200 mesh,’ and an API number like ‘API 140.’ They are not the same thing, and treating them as interchangeable is how rigs end up with screens that don't perform the way the box promised. One describes the weave; the other describes the cut. Only one of them is standardised.
What mesh count actually tells you
Mesh count is a weave specification: the number of openings per inch, counted in each direction. A 40-mesh screen has 40 openings per inch one way and 40 the other; a designation like 70×30 describes a rectangular weave. That is useful for describing the cloth — but it does not reliably tell you the size of particle the screen removes, because opening size depends on wire diameter, and layered or rectangular screens produce a spread of non-uniform openings that no single mesh number can capture.
The practical consequence shows up in the field constantly: two screens sold at the same mesh count can separate quite differently. One documented case had a panel bought as ‘API 80 / 80 mesh’ test out at API 140 — nearly twice as fine as the label implied. Selecting on mesh alone is selecting on the weave and hoping the cut follows. Matching the screen you actually need to the cut you are trying to make is a decision Rig IQ helps you set from your target, not from a mesh number on a box.
What the API Screen Number is
API RP 13C — internationally ISO 13501, and the replacement for the older RP 13E — fixed this by defining a standardised test and label. A representative section of the screen is mounted in a stack of calibrated ASTM sieves; a measured charge of dry aluminium oxide is sieved on a Ro-Tap, the run is repeated three times and averaged, and the result is the screen’s D100 cut point: the particle size above which nothing passes. That D100 is then matched to the ASTM sieve of nearest separation, and the screen is assigned an API Screen Number for the range its D100 falls into.
The important shift is from D50 to D100. The old RP 13E rated screens on D50 — the size at which half the particles are removed — while RP 13C rates on D100, the size at which effectively all are rejected. That change re-rated most screens: a cloth once called ‘200 mesh’ may carry an API number of only 100 to 140. But the payoff is comparability — every screen tested to RP 13C with the same API number removes solids of a similar size, whoever made it. Translating your target cut into the right API number is exactly the mapping Rig IQ is built to do.
Reading the label and selecting
An RP 13C label carries more than the API number. It also reports conductance in kilodarcies per millimetre — a measure of how freely fluid passes through the static screen, which stands in for flow capacity: all else equal, the higher-conductance screen processes more flow. And it reports the non-blanked (open) area. So a complete selection is a three-way trade: fine enough cut (API number), enough flow (conductance), enough open area to convey — not just ‘the finest screen that fits.’
The discipline, then, is to stop selecting on mesh and start selecting on the API number for the cut, cross-checked against conductance for the flow you need to handle. Go too fine on the API number without the conductance to pass your circulation rate and you flood the deck; match all three and the shaker does its job. Working that balance — cut versus flow versus your actual returns — from real numbers rather than a mesh label is precisely what Rig IQ is for.
Mesh vs API number
Mesh count = openings per inch (the weave). Does not reliably predict separation — same mesh can cut differently.
API Screen Number (RP 13C / ISO 13501) = the range the tested D100 cut point falls into (size above which nothing passes). Standardised, comparable across makers.
Rated on D100 now (was D50 under old RP 13E) — a former “200 mesh” may be API 100–140.
The label also shows conductance (kD/mm = flow capacity). Select on API number and conductance.
Mesh count describes a screen's weave — openings per inch — and does not reliably predict what it separates; two same-mesh screens can cut differently. The API Screen Number under RP 13C (ISO 13501) is the standardised D100 cut point, comparable across manufacturers. It is rated on D100 now, not the old D50, so a former “200 mesh” may be API 100–140. Select on the API number for the cut and conductance (kD/mm) for the flow — not on mesh.
Common questions
What is the difference between API screen number and mesh?
Mesh count is the number of openings per inch — it describes the screen's weave, not its separation, so two screens of the same mesh can cut differently. The API Screen Number, defined by API RP 13C, is the screen's tested D100 cut point expressed as a standardised range, so any RP 13C-tested screen with the same API number removes a similar particle size regardless of manufacturer.
What is the D100 cut point?
The D100 is the particle size above which nothing passes through the screen — the absolute cut. It is measured by a standardised RP 13C lab test: the screen is placed in a stack of calibrated ASTM sieves, dry aluminium oxide is sieved on a Ro-Tap three times and averaged, and the resulting cut point sets the API Screen Number. RP 13C uses D100, replacing the D50 basis of the older RP 13E.
Why might a 200-mesh screen be labelled API 140?
Because API RP 13C rates screens on the D100 cut point rather than the old D50, which re-rated most screens. A cloth historically called '200 mesh' often carries an API number of only 100 to 140 under the standardised test. The API number reflects tested separation, so it is the reliable basis for comparison and selection — not the mesh count.
