Common air purifier / box-fan filter sizes
| Nominal size | Actual (approx) | Typically used by |
|---|---|---|
| 16×25×1" | 15.7 × 24.7 × 0.75" | 5-Fan Luggable, many Corsi-Rosenthal boxes |
| 20×25×1" | 19.7 × 24.7 × 0.75" | 7-Fan XL Luggable, larger CR boxes |
| 16×20×1" | 15.7 × 19.7 × 0.75" | compact box builds |
| 20×20×1" | 19.7 × 19.7 × 0.75" | square box-fan builds |
| 6"/6.5" round | cylindrical | personal/desktop units (e.g. Exhalaron) |
Nominal vs actual — why filters read "16×25" but measure smaller
Furnace-filter sizes are nominal: a "16×25" filter actually measures about 15.7×24.7 inches so it slides into a 16×25 slot without jamming. Always buy by the printed nominal size, not the tape-measure figure.
How to measure your filter
- Read the size printed on the cardboard edge of the old filter first — it's almost always there.
- No print? Measure length × width × thickness in inches and round to the nearest standard size.
- Thickness matters: 1" is standard for box-fan/CR builds. Don't force a 2" filter into a 1" slot.
Which size should I buy?
If you run a Luggable or a 16×25 Corsi-Rosenthal box, you want 16×25×1. The 7-Fan XL and 20×25 boxes take 20×25×1. Both are standard MERV-13 sizes we stock — so you're never tied to one supplier.