Tee Loss Calculator

Inputs

Units

Choose a consistent unit system.

Flow rate (m³/h)

Pipe inside diameter (mm)

Fluid density (kg/m³)

Dynamic viscosity (mPa·s)

Pipe roughness (mm)

Use 0 for smooth pipe.

Gravity g (m/s²)

Number of tees

Tee selection

K depends on tee geometry and flow split.

Method

Both methods use the same core physics.

Friction factor source

Used to compute equivalent length.

Example Data Table

Scenario	Units	Flow	Diameter	Tee	K	Number	Typical total head loss
Chilled water run tees	SI	25 m³/h	100 mm	Standard run	0.60	2	≈ 0.17 m
Branch takeoff tees	SI	18 m³/h	80 mm	Standard branch (dividing)	1.80	3	≈ 0.87 m
Hydronic header tees	US	120 gpm	4 in	Swept run	0.30	4	≈ 0.28 ft

Example head losses are illustrative and depend on velocity.

Formula Used

Velocity: v = Q / A, where A = πD²/4.
Minor loss head (tee): h = K · v²/(2g).
Total head: h_total = h · N.
Pressure drop: ΔP = ρ g h_total.
Reynolds number: Re = ρ v D / μ.
Friction factor: f = 64/Re (laminar) or Swamee–Jain (turbulent).
Equivalent length: L_e = (K/f) · D.

How to Use This Calculator

Select SI or US units to match your project inputs.
Enter flow rate and inside diameter for the pipe section.
Choose a tee type and flow path that matches installation.
Provide fluid density and viscosity for operating conditions.
Set pipe roughness, or keep 0 for smooth pipe.
Enter the number of tees in the line segment.
Submit to see head loss and pressure drop above.
Download CSV or PDF to attach to design records.

Why Tee Loss Matters in Hydraulic Design

Tee fittings create separation and mixing that adds measurable resistance. In closed-loop hydronic or process lines, repeated tees can dominate the minor-loss budget. Quantifying head loss early helps confirm pump head, protect control valve authority, and avoid oversized equipment that wastes energy. It also improves bid accuracy when estimating pump power, pipe supports, and insulation loads.

Choosing Appropriate K Factors

K values depend on geometry, branch angle, flow split, and whether flow divides or combines. A straight-through run often has a lower K than a branch takeoff. Swept patterns reduce turbulence, while reducing tees can increase losses. When manufacturer data exists, prefer it over generic tables. If flow split is uncertain, bracket K using conservative and optimistic cases to bound design risk.

Using Equivalent Length for Network Modeling

Some designers convert K into equivalent length so tees can be modeled like extra pipe. The calculator estimates Le using Le = (K/f)·D, where f is the Darcy friction factor for the prevailing Reynolds number and roughness. This supports quick checks in spreadsheet takeoffs and aligns with common hydraulic solvers. Equivalent length is especially helpful when creating schedules, where fittings are counted but network models are not yet built.

Data Quality and Field Verification

Inputs drive accuracy. Use true inside diameter for the selected schedule and lining, and select density and viscosity for operating temperature. If water quality or glycol percentage changes, update properties. Field verification can include differential pressure readings across a representative branch or confirming balancing valve positions. For noisy systems, also check for cavitation, air entrainment, or partially closed isolation valves that can mask fitting losses.

Reporting and Review Practices

Document assumptions alongside results: tee type, flow path, K source, units, and number of fittings. Compare total minor losses against straight-pipe friction to identify sensitivity. During peer review, re-run key scenarios at minimum and maximum expected flow. Clear exported reports support submittals, commissioning, and future maintenance.

FAQs

1) What is “tee loss” in piping?

Tee loss is the added head loss caused by turbulence and flow separation in a tee fitting. It is commonly modeled with a K factor multiplied by velocity head.

2) Should I use run or branch K values?

Use run K when flow passes straight through the tee. Use branch K when flow turns into or out of the branch. Dividing and combining cases can differ.

3) Why does flow rate change the result?

Head loss scales with velocity squared. Increasing flow raises velocity, so the velocity head rises quickly and the tee loss increases nonlinearly.

4) When should I enter a custom K?

Enter a custom K when you have manufacturer data, test results, or project standards that better represent your fitting geometry, reducers, and operating flow split.

5) Is equivalent length always reliable?

Equivalent length is a convenient approximation tied to friction factor. It works well for early estimates, but detailed networks may prefer explicit K values at nodes.

6) What diameter should I use for accuracy?

Use the true inside diameter of the pipe where the tee is installed, accounting for schedule, lining, and corrosion allowance. Nominal size can mislead results.