How to measure your paint booth filter

Measure the frame, not the old filter. Old media shrinks, swells, and gets trimmed on site, so it lies about its own size. The steel opening the filter sits in is the truth. Measure the inside of the frame: width, then height, then depth if it's a panel holder with a channel.

The 4 inch rule for exhaust pads. Loose fiberglass and polyester exhaust media should be bigger than the opening. Take your frame measurement and add 4 inches to each face dimension. A 20 by 20 opening wants a 24 by 24 pad. The overhang wedges into the frame, holds the pad in place under airflow, and seals the edges so paint-loaded air can't slip past. An exact-size pad in an exhaust frame leaves gaps at the edges, and bypass is how overspray ends up in your fan and stack.

Panels and pleated filters are exact-size. Rigid frames (intake panels, AMU pre-filters, pocket bags, ceiling grid panels) are the opposite: they're built to the nominal frame size, so a 20 by 20 by 2 slot takes a 20 by 20 by 2 panel. Measure the frame channel and order the nominal size.

Rolls: width is what matters. Ceiling and intake roll media is cut to length on site. Measure the width of the plenum or wall section; common roll widths are 30, 36, and 48 inches.

What to do with the number. Take your measurement to the shop-by-size pages and pick the bucket that matches. If you have a part number instead of a tape measure, run it through the cross-reference lookup. If neither turns up your filter, send the number through a quote and we cross-check it against the brand and size paperwork WERCS keeps from two decades of service calls. That paperwork is how we confirm oddball fitments the catalogs miss.