User guide
Thank you for using the Gram Clean Air calculator. With this tool you always have the core of our work at your fingertips. This page explains every control on the calculator, in the order you normally use them.
Pick a formula
The calculator works in three modes, and you pick the one where the value you are missing is the answer. Diameter solves for the duct size from air volume and air velocity. Air velocity solves for m/s from an installed diameter and an air volume. Air volume solves for m³/h from a diameter and a velocity.
The field being calculated is greyed out and cannot be edited — it is the result. The remaining fields stay adjustable, so switching mode never loses your inputs.
Duct type
The duct type selector does not change any calculation. It only changes which standard sizes the "We recommend — Ø mm" buttons offer, so the size you land on is one you can order: the full range, the spiral-wound (Spiro) sizes, or the smaller transport sizes used for arms, hoses and point extraction.
Adjusting values
Every input has a slider for quick changes, a pencil icon for typing an exact number, and minus/plus buttons for stepping in fixed increments. Values are clamped to the range of the field, so you cannot enter a diameter or an air volume outside what the calculator supports.
Reading the result panel
The green panel always shows the duct diameter Ø in mm, the cross-sectional area A in m², the pressure loss per metre in Pa/m and the total pressure loss in Pa for the duct length you entered.
The duct length field does not affect diameter, velocity or air volume. It only converts the loss per metre into a total for that length of straight duct.
Recommended standard sizes
Below the result panel the calculator highlights the nearest standard duct size for the diameter you are working with. In the Air velocity and Air volume modes you can click any of these buttons to load that size straight into the calculation. In Diameter mode the buttons are shown but inactive, because the diameter is the result there.
Resetting
The reset icon in the header clears everything back to the starting values after a confirmation, so you can begin a new duct run without reloading the page.
Frequently asked questions
Why can I not edit one of the fields?
That field is the result of the formula you selected. Switch to a different formula if you want to enter that value yourself and calculate something else.
Does the duct type change the result?
No. It only changes the list of standard sizes offered as recommendations. The calculation is identical for every duct type.
What does the duct length field do?
It multiplies the pressure loss per metre into a total pressure loss in Pa for that length of straight duct. It does not change diameter, air velocity or air volume.
Are bends, filters and hoods included in the pressure loss?
No. The figures cover straight, clean ducting. Take component losses from the manufacturers' data sheets and add them to the total.
Can I use the calculator on a phone?
Yes. The layout adapts to small screens, and the same calculator is available as a mobile app on the App Store and Google Play.