Air Filters
Indoor Climate & Fixtures · 10 specs
Direct Answer
Residential HVAC furnace air filters standardize nominal dimensions (16×20×1", 16×25×1", 20×20×1", 20×25×1", 20×25×4") that measure 0.5 inches smaller in actual size, rated on the ASHRAE 52.2 MERV scale from MERV 1 to 16.
Source: ASHRAE Standard 52.2 (Method of Testing Air-Cleaning Devices) / EPA Guidelines · Last reviewed Aug 28, 2026
Specs
| Governing Standards | ASHRAE 52.2 / AHRI Standard 680 (Air Filter Sizing & Rating) |
| Actual vs Nominal Sizing | Actual dimensions are typically 0.50" (12.7 mm) smaller than nominal label |
| 16 × 20 × 1" Nominal | Actual: 15.5 × 19.5 × 0.75 inches (39.4 × 49.5 × 1.9 cm) |
| 16 × 25 × 1" Nominal | Actual: 15.5 × 24.5 × 0.75 inches (39.4 × 62.2 × 1.9 cm) | Common home size |
| 20 × 20 × 1" Nominal | Actual: 19.5 × 19.5 × 0.75 inches (49.5 × 49.5 × 1.9 cm) | Return air grilles |
| 20 × 25 × 1" Nominal | Actual: 19.5 × 24.5 × 0.75 inches (49.5 × 62.2 × 1.9 cm) | Universal residential |
| 20 × 25 × 4" Media Filter | Actual: 19.75 × 24.25 × 4.38 inches | Deep pleated cabinet filter (6–12 mo life) |
| MERV 8 (Residential Standard) | Captures 70–85% of particles 3.0–10 µm (Dust mites, pollen, mold spores) |
| MERV 11 (Pet & Allergy) | Captures 65–79% of 1.0–3.0 µm + 85% of 3–10 µm (Pet dander, auto emissions) |
| MERV 13 (High-Efficiency) | Captures >50% of 0.3–1.0 µm + >85% of 1.0–3.0 µm (Bacteria, virus carriers, smoke) |
ASHRAE MERV Rating Scale & Particle Capture Matrix
| MERV Rating | MPR (3M) | FPR (Home Depot) | Particle Size Capture | Primary Contaminants Trapped | Recommended Filter Replacement | | :---: | :---: | :---: | :---: | :---: :---: | | MERV 1–4 | <300 | — | <20% (3.0–10,µm) | Large lint, carpet fibers, standing dust | Every 30 days | | MERV 8 | 600 | 5 | 70–85% (3.0–10,µm) | Pollen, dust mites, mold spores, hair | Every 60–90 days (Residential baseline) | | MERV 11 | 1000–1200 | 7 | 65–79% (1.0–3.0,µm) | Pet dander, smog, auto exhaust, fine dust | Every 90 days | | MERV 13 | 1500–1900 | 10 | >50% (0.3–1.0,µm) | Bacteria, smoke, virus droplets, sneeze particles| Every 90 days (Check HVAC static pressure) | | MERV 16 / HEPA| 2800+ | — | >95% to 99.97% (0.3,µm) | Hospital surgical suites, cleanrooms | 6 to 12 months (Dedicated media cabinets) |