Scroll down to use our web calculator or try our mobile app.

How to use the calculator

1. Choose your shape on the right hand side.
2. Choose the units you’re most comfortable with: m³/h, l/s or CFM
3. Decide how you want to select your duct – then grab the sliders and move them until you have the information you need.

Velocity slider colours

Red = Too much velocity
Green = Generally in spec for Prihoda Fabric Ducts
Blue = A comfortable selection



If you have 1000l/s and you want a velocity of 5m/s: select “l/s, mm, m/s” and input 1000 into the Airflow box. Then adjust the Velocity slider to 5m/s. Looking at the Size A box, it suggests a diameter of 520mm. As everything is made to order, we can make a 520mm duct. You can also input 500mm into the duct size box for a standard duct size and you’ll see that it moves the velocity to 5.1m/s.

The Distribution graph shows air velocity at isothermal conditions using a band of micro-perforation diffusers laser cut onto the duct. You can set the band angle as you wish: the narrower the band, the higher the velocity. Please contact us for a firm diffuser selection, as we offer a range of diffuser types that are suitable for specific application requirements. Microperforations are best used for make up air, cooling only, or high air volume such as food or lab applications.

Please note: the calculator is for guidance only. We do not take responsibility for your duct selections or sizes using this software; we always recommend you discuss specific selections with us.

Download the Prihoda calculator Android app

Download the Prihoda calculator iOS app