How do you size a cyclone dust collector?

From the duct: give the cyclone inlet the duct's area and take every other dimension as a fraction of the body diameter. With Stairmand's high-efficiency proportions, the body is 2.8 times the duct: a 6 in duct gives a 16.8 in body, 67.3 in tall overall.

What are the Stairmand cyclone proportions?

For the high-efficiency cyclone: inlet 0.5 D high and 0.2 D wide, outlet tube 0.5 D across reaching 0.5 D inside, cylinder 1.5 D high, overall height 4 D and dust outlet 0.375 D, D being the body diameter.

How do I make the cone of a cyclone?

It is a frustum from the body diameter down to the dust outlet: develop it as a cone sector. For the 6 in example, from 427.1 mm to 160.2 mm over 1067.8 mm; the cone page gives the two radii, the angle and the full-size template.

Where does the inlet go?

Tangent to the body, at the top, right under the top plate: the outer wall of the inlet runs flush with the body so the air enters along the wall. The slot in the body is a rectangle a high along the top edge.

Is this Bill Pentz's design?

No. Pentz publishes his own proportions and a spreadsheet for his cyclones. This page uses the proportions Stairmand and Lapple published for cyclone separators, and develops each sheet of whatever size they give.

DIY cyclone dust collector plans: every sheet of the cyclone from the Stairmand proportions, for any duct size

Updated on 03 November 2026

A cyclone separator spins the dusty air round inside a cylinder: the chips and dust are thrown to the wall and slide down the cone into a bin, and the cleaner air leaves up the middle through the outlet tube, to the blower and the filter. In a woodworking shop it saves the filter and keeps the suction up, and it is built from a handful of sheet metal parts: the body, the cone, the outlet tube, the top, the inlet and, in many designs, an inlet ramp.

This page sizes the cyclone from your duct, by the proportions Stairmand and Lapple published for cyclone separators, and opens each sheet already worked out, with its flat pattern and a full-size template. Bill Pentz's well-known DIY design uses proportions of its own; the method here is the classic one from the industrial literature.

Cyclone calculator

Type the duct diameter: the blower inlet, or the main hose the cyclone sits on. The body diameter comes out so that the inlet has the same area as the duct; type it instead if you already have a drum or a size in mind. Each sheet in the list opens with these measurements.

Duct diameter (blower inlet or main hose)

Body diameter, optional

Proportions

Sheet thickness

Unit

Body diameter, D	–
Inlet, height × width	–
Outlet tube, diameter × length inside	–
Cylinder height	–
Cone height	–
Overall height	–
Dust outlet diameter	–

The proportions are fractions of the body diameter, as Stairmand and Lapple published them. Leave the body diameter blank and it comes from the duct: the inlet gets the area of the duct. Each link opens the part already worked out, with its flat pattern, in millimetres.

Embed this calculator on your site

Free, and it works on any site: paste the code where you want the calculator. It links back to this guide.

<iframe src="https://planichapa.com/en/embed/cyclone" width="100%" height="1000" style="border:0;max-width:100%" loading="lazy" title="DIY cyclone dust collector plans: every sheet, any size"></iframe>

The proportions

Every dimension of a cyclone is a fraction of its body diameter D. These are the three classic sets:

	Stairmand, high efficiency	Lapple, conventional	Stairmand, high throughput
Inlet height, a	0.5 D	0.5 D	0.75 D
Inlet width, b	0.2 D	0.25 D	0.375 D
Outlet tube diameter, De	0.5 D	0.5 D	0.75 D
Outlet tube length inside, S	0.5 D	0.625 D	0.875 D
Cylinder height, h	1.5 D	2 D	1.5 D
Overall height, H	4 D	4 D	4 D
Dust outlet, B	0.375 D	0.25 D	0.375 D

The high-efficiency set separates finer dust at a given air speed; the high-throughput set moves more air through a smaller cyclone. For a woodworking shop, the high-efficiency one is the usual start.

Body from the duct: a × b = π × d² / 4 → D = √( π d² / (4 × a/D × b/D) ) With the Stairmand high-efficiency set, a × b = 0.1 D², so D = 2.80 d: a 6 in duct gives a 16.8 in (427.1 mm) body.

The sheets

The body is a cylinder of diameter D and height h, rolled from a sheet π (D − t) long. The inlet is tangential: the outer wall of the inlet duct runs flush with the body, so the slot in the body is a rectangle a high, along the top edge, and Rm × acos((Rm − b)/Rm) wide on the flat sheet, Rm being the mid-thickness radius.
The cone runs from D at the top to the dust outlet B, over H − h. Its pattern is the cone sector.
The outlet tube is a cylinder of diameter De, reaching S below the top and up through it to the blower.
The top is a flat ring, D outside with a De hole for the outlet tube.
The inlet goes from the round duct to the a × b rectangle through a rectangle to round transition.
An inlet ramp, one turn of a screw flight round the outlet tube at a pitch of a, starts the spiral and keeps the incoming air from hitting the stream that has already turned.

Worked example

A 6 in (152.4 mm) duct, Stairmand high efficiency, in 1 mm sheet:

	mm	in
Body diameter, D	427.1	16.81
Inlet, a × b	213.6 × 85.4	8.41 × 3.36
Outlet tube, De × S	213.6 × 213.6	8.41 × 8.41
Cylinder height, h	640.7	25.22
Cone height, H − h	1067.8	42.04
Overall height, H	1708.4	67.26
Dust outlet, B	160.2	6.31

The body sheet is π × 426.1 = 1338.6 mm by 640.7 mm, with the inlet slot 213.6 mm high and 197.8 mm wide at the top edge. A 4 in duct gives an 11.2 in (284.7 mm) body, 1138.9 mm overall.

Frequently asked questions

How do you size a cyclone dust collector?: From the duct: give the cyclone inlet the duct's area and take every other dimension as a fraction of the body diameter. With Stairmand's high-efficiency proportions, the body is 2.8 times the duct: a 6 in duct gives a 16.8 in body, 67.3 in tall overall.
What are the Stairmand cyclone proportions?: For the high-efficiency cyclone: inlet 0.5 D high and 0.2 D wide, outlet tube 0.5 D across reaching 0.5 D inside, cylinder 1.5 D high, overall height 4 D and dust outlet 0.375 D, D being the body diameter.
How do I make the cone of a cyclone?: It is a frustum from the body diameter down to the dust outlet: develop it as a cone sector. For the 6 in example, from 427.1 mm to 160.2 mm over 1067.8 mm; the cone page gives the two radii, the angle and the full-size template.
Where does the inlet go?: Tangent to the body, at the top, right under the top plate: the outer wall of the inlet runs flush with the body so the air enters along the wall. The slot in the body is a rectangle a high along the top edge.
Is this Bill Pentz's design?: No. Pentz publishes his own proportions and a spreadsheet for his cyclones. This page uses the proportions Stairmand and Lapple published for cyclone separators, and develops each sheet of whatever size they give.