# Getting started

Source: https://meptools.com/tools/duct-pressure-drop-calculator/docs/getting-started/

Open **Duct Pressure Drop Calculator** from the [tools catalog](/docs/tools-catalog). No sign-in
is needed to calculate — you only need an account to save projects or export a PDF report.

The page is a single screen: five input cards (airflow & duct run, geometry, material & air
properties, fittings, and a duct schematic that sketches the run as you type), followed by the
result once you calculate one. Nothing computes on its own — enter your inputs, then press
**Calculate**. Once a result is on screen, editing any input marks it **stale** and swaps the
button to **Recalculate**, so you are never looking at a result that no longer matches the form.

## The fast path: Load a worked example

Before your first calculation, the start zone offers **Load a worked example**. It fills in a
400 × 300 mm rectangular galvanised-steel main carrying 0.5 m³/s over 15 m, with a manual **Σ K**
of `2.4` and the **Main duct** advisory role, and runs it immediately. Use it to see a populated
result before typing anything of your own. The button is hidden once you arrive via a share
link or a restored draft, and it disappears after your first **Calculate**.

![Duct Pressure Drop Calculator after Calculate, showing a populated result panel](./_assets/duct-getting-started-flow.png)

## A worked example (typed by hand)

These are different numbers from the one-click example above — a second, independently
verified case if you want to enter values yourself. Enter the following into the four input
cards, then press **Calculate**:

| Card                         | Field                           | Value                              |
| ---------------------------- | ------------------------------- | ---------------------------------- |
| 01 Airflow & duct run        | Airflow (Q)                     | `0.75` m3/s                        |
| 01 Airflow & duct run        | Duct length (L)                 | `30` m                             |
| 02 Duct geometry             | Shape                           | Rectangular                        |
| 02 Duct geometry             | Width (w)                       | `500` mm                           |
| 02 Duct geometry             | Height (h)                      | `300` mm                           |
| 03 Material & air properties | Roughness preset                | Galvanised steel (0.15 mm)         |
| 03 Material & air properties | Air temperature / pressure      | `20` °C / `101.325` kPa (defaults) |
| 04 Fittings                  | Mode                            | Manual Σ K                         |
| 04 Fittings                  | Total fitting coefficient (Σ K) | `1.5`                              |

The result panel should now read:

| Output              | Value                               |
| ------------------- | ----------------------------------- |
| Total pressure drop | **46.2 Pa** (≈ 4.71 mmH₂O)          |
| Friction rate       | 0.787 Pa/m                          |
| Straight duct       | 23.6 Pa                             |
| Fittings            | 22.6 Pa                             |
| Velocity            | 5 m/s (the gauge marker reads 5.00) |
| Reynolds            | 124,494 (turbulent)                 |
| Friction factor     | 0.01872                             |

If your numbers differ, check the airflow **unit selector** first — it sits inside the airflow
field and defaults to `m3/s`, so a value meant as L/s is 1000× too large.

## Add an advisory band

In **Manual Σ K** mode, set **Duct role (advisory)** to `Main duct - 5-8 m/s`. The velocity
gauge now draws the 5–8 m/s band and reports **Within advisory band** for the 5 m/s above.
The band is advisory only: it never changes the calculated pressure drop, it only produces a
verdict and a warning when you fall outside it.

## Then

- Swap Σ K for a real [fitting schedule](/tools/duct-pressure-drop-calculator/docs/fittings) —
  pick fittings from the library, set quantities, override any K you disagree with.
- Read [the result panel in detail](/tools/duct-pressure-drop-calculator/docs/results),
  including the warnings and the six evidence blocks (**Pressure split**, **Fittings & valves**,
  **Calculation steps**, **Assumptions & warnings**, **Formulas & references**, **Report**).
- [Copy, share or export](/tools/duct-pressure-drop-calculator/docs/exporting-and-saving) the
  calculation.