Press systems · Zeta values
Zeta values of press connectors: what a fitting costs in pressure
Every elbow, every tee and every reducer takes energy from the flow – the resistance coefficient zeta (ζ) says how much. For the pipe-network calculation to DIN 1988-300 the designer needs these values per fitting and size, and the manufacturers measure them to DVGW code of practice W 575. This page explains the quantity, shows the values of the Viega and Geberit systems we carry from the data layer and works out what a chain of reducers costs compared with a single reducer.
- Formula
- Δp = ζ · ρ/2 · v²
- Measurement basis
- DVGW code of practice W 575 (manufacturer statement)
- Elbow 90°
- about 0.4–1.0 depending on size
- Tee branch
- about 1.0–2.2 (small sizes higher)
- Coupling
- about 0.2–0.7
- Source
- Viega sheets 03/2022 and 07/2026, Geberit sheets 03/2021; Sanha: on request
What the zeta value is
The resistance coefficient ζ is a dimensionless number that relates the pressure loss of a component to the kinetic energy of the flow: Δp = ζ · ρ/2 · v², with the density ρ of the medium and the flow velocity v in the pipe. An elbow with ζ = 1.0 costs around 2 kPa (20 mbar) with water at 2 m/s, at 1 m/s only a quarter of that – the pressure loss grows with the square of the velocity. Alternatively, manufacturers express the resistance as an equivalent pipe length: the length of straight pipe that would have the same pressure loss (leq = ζ · d / λ).
Zeta values depend on shape and size, not on the material: a 90° elbow in 15 mm has a different value from the same elbow in 54 mm, because the ratio of bend radius to diameter and the inner contour of the connector change. With tees the flow routing comes into it: branch, run and counterflow, each for dividing and combining flow, have their own values – the branch with dividing flow is almost always the most expensive.
Why the manufacturers measure For the pipe-network calculation to DIN 1988-300 blanket zeta values from reference tables may be used – or the measured values of the system manufacturer. Measurement follows DVGW code of practice W 575, which lays down test set-up and evaluation. Manufacturer values are usually lower than the blanket values, because the inner contour of a press connector is more favourable to flow than the reference tables assume; that allows smaller sizes or lower pump power.
Zeta value is not Z dimension. The zeta value (ζ) is the dimensionless pressure-loss coefficient of a fitting for the pipe-network calculation. The Z dimension, by contrast, is a length: the distance from the centre of the fitting to the pipe end in the socket, which the fitter subtracts from the centre-line dimension when cutting to length. Both are in the manufacturer's documents, both are tied to the manufacturer with press systems – but one belongs to the designer, the other to the fitter and, over the years, to the maintenance engineer: replacement parts fit only with the same Z dimension (see Press systems – From our practice).
The values of the Viega systems we carry
The tables come from our data layer, which takes over the manufacturers’ sheets verbatim: Viega zeta values press connection systems (03/2022, to DVGW W 575) for the system-pipe systems, the Megapress sheet (07/2026) with zeta, equivalent pipe length and measured pressure loss per model, and the Geberit sheets “resistance coefficients for fittings and connectors” (03/2021) for FlowFit and Mepla. Size = outside diameter of the pipe in mm, for Megapress in inch. A dash means: no value is given in the sheet for this size and this fitting.
Viega Profipress (copper)
| Dimension (mm) | elbow / bend 90° | elbow / bend 45° | coupling / socket | T-piece, branch (flow separation) | T-piece, run (flow separation) | T-piece, counter-flow (flow separation) | T-piece, branch (flow merging) | T-piece, run (flow merging) | T-piece, counter-flow (flow merging) | reducer |
|---|---|---|---|---|---|---|---|---|---|---|
| 12 | 0.9 | 0.7 | 0.2 | 1.1 | 0.4 | 1.0 | 2.4 | 4.5 | 2.3 | – |
| 15 | 0.5 | 0.6 | 0.7 | 2.1 | 0.9 | 1.4 | 1.6 | 3.3 | 1.9 | 1.5 |
| 18 | 0.6 | 0.4 | 0.3 | 2.2 | 0.7 | 1.3 | 1.5 | 3.0 | 2.0 | 1.5 |
| 22 | 0.4 | 0.3 | 0.1 | 1.0 | 0.7 | 0.7 | 1.5 | 2.8 | 2.0 | 1.0 |
| 28 | 0.2 | 0.2 | 0.6 | 1.7 | 0.7 | 0.9 | 1.3 | 2.6 | 1.8 | 1.6 |
| 35 | 0.5 | 0.4 | 0.8 | 1.6 | 0.5 | 0.8 | 1.0 | 1.7 | 1.1 | 1.4 |
| 42 | 0.4 | 0.2 | 0.1 | 0.9 | 0.1 | 0.9 | 1.4 | 2.8 | 1.4 | 0.1 |
| 54 | 0.4 | 0.2 | 0.1 | 0.9 | 0.1 | 0.9 | 1.4 | 2.8 | 1.4 | 0.1 |
| 64.0 | 0.3 | 0.2 | 0.1 | 0.9 | 0.1 | 0.9 | 1.9 | 3.8 | 1.8 | 0.1 |
| 76.1 | 0.2 | 0.1 | 0.1 | 1.1 | 0.1 | 1.1 | 1.8 | 3.5 | 2.4 | 0.1 |
| 88.9 | 0.2 | 0.1 | 0.1 | 1.1 | 0.1 | 1.1 | 1.8 | 3.5 | 2.4 | 0.1 |
| 108.0 | 0.2 | 0.1 | 0.1 | 1.1 | 0.1 | 1.1 | 1.8 | 3.5 | 2.4 | 0.1 |
Viega Sanpress (gunmetal on stainless-steel pipe)
| Dimension (mm) | elbow / bend 90° | elbow / bend 45° | coupling / socket | T-piece, branch (flow separation) | T-piece, run (flow separation) | T-piece, counter-flow (flow separation) |
|---|---|---|---|---|---|---|
| 15 | 0.7 | 1.3 | 0.4 | 2.0 | 0.7 | 1.1 |
| 18 | 1.1 | 1.4 | 0.4 | 1.9 | 0.6 | 0.7 |
| 22 | 1.0 | 1.6 | 0.4 | 0.9 | 0.4 | 0.7 |
| 28 | 1.3 | 0.4 | 0.5 | 1.6 | 0.5 | 0.8 |
| 35 | 1.6 | 0.4 | 1.1 | 1.5 | 0.5 | 0.6 |
| 42 | 0.4 | 0.3 | 0.1 | 0.8 | 0.1 | 0.8 |
| 54 | 0.4 | 0.3 | 0.1 | 0.8 | 0.1 | 0.8 |
| 76.1 | 0.6 | 0.3 | 0.1 | 0.8 | 0.1 | 0.8 |
| 88.9 | 0.6 | 0.3 | 0.1 | 0.8 | 0.1 | 0.8 |
| 108.0 | 0.6 | 0.3 | 0.1 | 0.8 | 0.1 | 0.8 |
| 12 | 0.4 | – | 0.2 | – | – | – |
Viega Sanpress Inox (stainless steel)
| Dimension (mm) | elbow / bend 90° | elbow / bend 45° | coupling / socket | T-piece, branch (flow separation) | T-piece, run (flow separation) | T-piece, counter-flow (flow separation) |
|---|---|---|---|---|---|---|
| 15 | 0.5 | 1.5 | 0.4 | 2.0 | 0.7 | 1.2 |
| 18 | 0.6 | 1.6 | 0.4 | 2.3 | 0.6 | 1.2 |
| 22 | 0.4 | 0.5 | 0.4 | 1.2 | 0.3 | 1.0 |
| 28 | 0.2 | 0.3 | 0.6 | 2.0 | 0.6 | 1.3 |
| 35 | 0.5 | 0.2 | 1.2 | 1.5 | 0.4 | 1.0 |
| 42 | 0.4 | 0.2 | 0.1 | 1.0 | 0.1 | 1.0 |
| 54 | 0.4 | 0.2 | 0.1 | 0.9 | 0.1 | 0.9 |
| 64.0 | 0.3 | 0.2 | 0.1 | 1.0 | 0.1 | 1.0 |
| 76.1 | 0.2 | 0.1 | 0.1 | 1.1 | 0.1 | 1.1 |
| 88.9 | 0.2 | 0.1 | 0.1 | 1.0 | 0.1 | 1.1 |
| 108.0 | 0.2 | 0.1 | 0.1 | 1.1 | 0.1 | 1.1 |
Viega Raxofix (multilayer pipe)
| Dimension (mm) | elbow / bend 90° | elbow / bend 45° | coupling / socket | T-piece, branch (flow separation) | T-piece, run (flow separation) | T-piece, counter-flow (flow separation) |
|---|---|---|---|---|---|---|
| 16 | 4.7 | – | 3.7 | 2.6 | 0.8 | 2.8 |
| 20 | 1.4 | – | 1.2 | 1.6 | 1.0 | 2.0 |
| 25 | 1.2 | 1.6 | 0.5 | 1.3 | 0.8 | 1.2 |
| 32 | 1.6 | 1.4 | 1.0 | 1.8 | 0.5 | 1.8 |
| 40 | 0.9 | 0.7 | 0.5 | 1.1 | 0.7 | 1.1 |
| 50 | 0.8 | 0.6 | 0.4 | 1.0 | 0.6 | 1.0 |
| 63 | 0.8 | 0.5 | 0.3 | 0.8 | 0.5 | 0.8 |
Viega Megapress (thick-walled steel pipe, inch)
Show full table · more than 20 rows
| Dimension (inch) | elbow / bend 90° | elbow / bend 45° | coupling / socket |
|---|---|---|---|
| ⅜ | 0.84 | 0.80 | 0.50 |
| ½ | 0.83 | 0.80 | 0.46 |
| ¾ | 0.61 | – | – |
| 1 | 0.64 | 0.54 | 0.29 |
| 1¼ | 0.51 | 0.38 | 0.26 |
| 1½ | 0.45 | 0.32 | 0.22 |
| 2 | 0.48 | 0.35 | 0.22 |
| 2½ | 0.47 | 0.38 | 0.3 |
| 3 | 0.46 | 0.37 | 0.29 |
| 4 | 0.44 | 0.36 | 0.28 |
| ¾ | 0.58 | 0.51 | 0.32 |
| 3/4 x ½ x 3/4 | – | 0.38 | – |
| 1x½x1 | – | 0.42 | – |
| 1x¾x1 | – | 0.42 | – |
| 1¼ x ½ x 1¼ | – | 0.32 | – |
| 1¼ x ¾ x 1¼ | – | 0.32 | – |
| 1¼ x 1 x 1¼ | – | 0.32 | – |
| 1¼ x 1 | – | – | 0.35 |
| 1½ x ½ | – | – | 0.39 |
| 1½ x ¾ | – | – | 0.35 |
| 1½ x 1 | – | – | 0.35 |
| 1½ x 1¼ | – | – | 0.26 |
| 2x½ | – | – | 0.41 |
| 2x¾ | – | – | 0.35 |
| 2x1 | – | – | 0.35 |
| 2 x 1¼ | – | – | 0.29 |
| 2 x 1½ | – | – | 0.26 |
| 3/4 x ½ | – | – | 0.42 |
| 1x½ | – | – | 0.41 |
The Megapress sheet additionally lists tees with reduced branch (say 1 × ½ × 1) as well as the equivalent pipe lengths and the measured pressure losses per model; these rows are in the data layer and are supplied as a table on request.
The values of the Geberit systems we carry
Geberit publishes one sheet per system with 15 fittings in the order of the DVGW W 575 codes – tees at flow separation and merging, bends, reducer, wall plates, distributor, coupling. The multilayer systems show markedly higher values than metal systems of the same size, because the support sleeve sits inside the pipe and narrows the cross-section: a Mepla 90° bend in d 16 costs ζ = 15.0, a Profipress bend in 15 mm 0.5. For reduced tees, according to Geberit, the value of the equal tee with the smallest size of the reduced piece applies.
Geberit FlowFit (multilayer pipe)
| Dimension (mm) | elbow / bend 90° | elbow / bend 45° | coupling / socket | T-piece, branch (flow separation) | T-piece, run (flow separation) | T-piece, counter-flow (flow separation) | T-piece, branch (flow merging) | T-piece, run (flow merging) | T-piece, counter-flow (flow merging) | reducer |
|---|---|---|---|---|---|---|---|---|---|---|
| 16 | 3.2 | – | 1.8 | 4.2 | 2.6 | 4.2 | 9.6 | 16.5 | 9.2 | – |
| 20 | 1.5 | – | 0.9 | 2.4 | 1.1 | 2.4 | 4.8 | 7.7 | 6.8 | 1.2 |
| 25 | 1.2 | 3.2 | 0.7 | 1.9 | 0.8 | 1.9 | 3.3 | 5.1 | 4.5 | 0.7 |
| 32 | 1.0 | 2.9 | 0.5 | 1.7 | 0.6 | 1.7 | 2.7 | 4.0 | 3.2 | 0.5 |
| 40 | 1.5 | 2.2 | 0.4 | 1.4 | 0.4 | 1.4 | 1.9 | 2.9 | 3.1 | 0.4 |
| 50 | 1.8 | 2.7 | 0.5 | 1.5 | 0.5 | 1.5 | 2.3 | 3.4 | 4.0 | 0.3 |
| 63 | 1.6 | 2.7 | 0.4 | 1.3 | 0.4 | 1.3 | 1.9 | 2.8 | 3.7 | 0.4 |
| 75 | 1.5 | 2.4 | 0.3 | 1.2 | 0.2 | 1.2 | 1.6 | 2.3 | 3.1 | 0.4 |
Geberit Mepla (multilayer pipe)
| Dimension (mm) | elbow / bend 90° | elbow / bend 45° | coupling / socket | T-piece, branch (flow separation) | T-piece, run (flow separation) | T-piece, counter-flow (flow separation) | T-piece, branch (flow merging) | T-piece, run (flow merging) | T-piece, counter-flow (flow merging) | reducer |
|---|---|---|---|---|---|---|---|---|---|---|
| 16 | 15.0 | – | 4.1 | 15.0 | 4.8 | 15.0 | 21.5 | 46.2 | 33.0 | – |
| 20 | 9.0 | – | 2.3 | 9.0 | 2.6 | 9.0 | 13.3 | 28.6 | 20.7 | 2.8 |
| 26 | 7.0 | 2.9 | 1.3 | 7.0 | 1.4 | 7.0 | 9.7 | 20.8 | 15.3 | 1.8 |
| 32 | 4.7 | 1.9 | – | 4.7 | 1.0 | 4.7 | 6.5 | 14.2 | 10.5 | 1.3 |
| 40 | 4.3 | 1.6 | 0.6 | 4.3 | 0.9 | 4.3 | 5.5 | 11.9 | 8.9 | 0.8 |
| 50 | 4.0 | 1.3 | 0.5 | 4.0 | 0.6 | 4.0 | 5.1 | 11.1 | 8.3 | 0.6 |
| 63 | 4.1 | 1.9 | 0.7 | 4.1 | 0.9 | 4.1 | 6.4 | 13.9 | 10.3 | 0.4 |
| 75 | 5.3 | 2.2 | 0.9 | 5.3 | 1.1 | 5.3 | 7.7 | 16.6 | 12.3 | 0.6 |
Wall plates, double wall plates and floor distributors of the Geberit sheets are in the data layer and are supplied on request. In the Mepla sheet the coupling value for d 32 is an obvious misprint (“08”); that cell stays empty until Geberit confirms the value. For Sanha NiroSan, SANHA-Press and the Victaulic couplings we hold no zeta sheets – the manufacturers carry them in their planning documents; we request them for your project.
From practice: what a chain of reducers costs
An example with the values above: reducing from 54 to 22 mm can be done in one fitting if the system carries the reducer 54 × 22 – one zeta value, two pressings. If a supplier carries only basic shapes, this becomes a chain 54 × 42, 42 × 28, 28 × 22: three zeta values, six pressings, three times the installation time per joint (cost comparison calculator) and three times the overall length. That is the hydraulic and economic reason behind our experience value of carrying systems with a wide range: it is not the single zeta value that decides, but how many fittings a task needs.
For the design: use the manufacturer's zeta values when the system is fixed, otherwise the blanket values of DIN 1988-300; limit velocities to the standard (the pressure loss grows quadratically); arrange tees so that the main flow stays in the run.
Further reading
Tools of this section: System finder (which system suits medium, pipe and size) · Joining methods compared · Cost comparison calculator · Press systems overview.
The cross-cutting topics: Mixed installation and corrosion · Press profiles and tools · Seals and media · Leak testing and SC-Contur
Frequently asked questions on zeta values
How do I calculate the pressure loss of a fitting with the zeta value?
Pressure loss = zeta × density × velocity² / 2 - the tool gives the zeta value per fitting and size as stated by the manufacturer and calculates the pressure loss for your flow.
What is the zeta value of a press connector?
The resistance coefficient ζ with which the pressure loss of the fitting is calculated: Δp = ζ · ρ/2 · v². The manufacturers measure it per fitting and size to DVGW W 575.
Are the zeta values for copper and stainless steel the same?
Not quite: they depend on the inner contour of the connector, not on the material. Profipress and Sanpress Inox of the same size lie close together but are measured separately.
Where do I find the zeta values for Sanha?
In the manufacturer's planning documents; in house we currently hold the Viega and the Geberit sheets. We request the Sanha values for your project.
Why are the zeta values of the multilayer systems so much higher?
Because the support sleeve of the fitting sits inside the pipe and narrows the free cross-section – a Mepla or FlowFit bend in d 16 is at ζ 3 to 15, a metal press bend of the same nominal size below 1. For the pipe-network calculation this means: think one size larger for multilayer pipe, or use the manufacturer values.
Why does the tee branch have the highest value?
Because the flow is turned through 90° and divided; with dividing flow in the branch the values lie between 1 and over 2 depending on size.
What is the equivalent pipe length?
The length of straight pipe that would have the same pressure loss as the fitting – Viega states it for Megapress per model.
May I use manufacturer values in the calculation to DIN 1988-300?
Yes, if the system is fixed. Otherwise one calculates with the blanket values of the standard.
Zeta values for your project?
Tell us system, sizes and fittings – we compile the manufacturer values, also for the systems whose sheets are not yet shown here.
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Sources: Viega zeta values press connection systems (to DVGW W 575, 03/2022), Viega Megapress zeta values and pipe equivalents (07/2026), Viega planning manual industrial technology 08/2026, Geberit resistance coefficients for fittings and connectors FlowFit and Mepla (03/2021); DIN 1988-300, DVGW W 575. Zickwolff experience values (class E) of 2026-09-24.