How long is a bedbug? - briefly
A typical bedbug measures approximately 4–5 mm (0.16–0.20 in) in length. This size places it among the larger members of the true bug order.
How long is a bedbug? - in detail
Adult bed bugs typically measure between 4.5 mm and 5.5 mm in length (approximately 0.18–0.22 in). This size applies to fully fed individuals; unfed adults are slightly shorter, averaging 4.2 mm. Nymphal stages show a progressive increase in length:
- First‑instar nymph: 1.2 mm
- Second‑instar nymph: 1.8 mm
- Third‑instar nymph: 2.5 mm
- Fourth‑instar nymph: 3.3 mm
- Fifth‑instar nymph (pre‑adult): 4.0 mm
Eggs are markedly smaller, measuring 0.9 mm × 0.5 mm. After a blood meal, an adult can expand up to 30 % in overall volume, but the linear dimension changes only marginally.
Measurements are obtained with calibrated stereomicroscopes or digital imaging systems, employing micrometer scales for precision. Reported ranges derive from multiple entomological surveys across temperate regions, confirming that size variation correlates with feeding status, species strain, and environmental temperature.
For reference, the common housefly (Musca domestica) averages 6–7 mm, making the bed bug slightly shorter but comparable in overall body plan. The described dimensions provide a reliable baseline for identification, monitoring, and control efforts.