I'm not sure what size to order...

To ensure a proper fit, measure your vent pipe's outside diameter (O.D.) and use the following table. Vent Pipe Manufacturers size their pipe by the inside diameter (I.D.). Because OdorHogs fit over the outside of your vent pipe, we care what the outside diameter is. The O.D. you measure will be slightly larger than the actual filter size you order. This tells us whether you have a “standard thickness” of pipe and that your OdorHog will fit properly.

If you have metal or cast iron pipes, be sure to order the clamp-on style so it has more flexibility in fitting your non-standard size pipes.