The Trane / American Standard BAYFTAH26M (TFM265) whole-house filter is labeled “21x26x5” but actually measures ~19.87 x 25.25 x 4.87 inches. Unlike 1″ filters, 4″/5″/6″ whole-house filters don't share one universal nominal-to-actual conversion — always match by brand and model, not just the printed size.
A genuinely different Trane Perfect Fit cabinet size than BAYFTAH23M — sources vary slightly on the exact figure, so confirm against your cabinet. No manufacturer spec sheet found for this exact figure — based on consistent independent reseller measurements.
Match by brand + model, not nominal size. Confirm against your old filter or equipment manual before ordering.
Looking for a 1″ furnace filter instead? Use the full FilterKey tool.