Bridging Distance Calculator

Bridging in 3D printing refers to the process of extruding filament across an open gap between two support points, without any material beneath it. The extruded plastic must span the distance in mid-air and solidify before it sags too much. Getting clean bridges is one of the trickier aspects of FDM printing, and the maximum reliable distance depends on several interrelated factors.

The nozzle diameter affects bridging because a larger nozzle produces a thicker strand of filament. Thicker strands are heavier but also have more structural rigidity. A standard 0.4 mm nozzle is the most common starting point. Smaller nozzles (0.2 to 0.3 mm) can sometimes bridge shorter distances more cleanly because the thinner strands cool faster.

Layer height plays a critical role. A lower layer height relative to the nozzle diameter produces a flatter, wider extrusion that cools more quickly and resists sagging. A layer height of 50 percent of the nozzle diameter or less is generally recommended for bridging. For a 0.4 mm nozzle, that means a 0.2 mm layer height or lower.

Print speed during bridging should typically be slower than normal printing speed. Slower speeds give the filament more time to cool and solidify before it stretches under gravity. Most slicers recommend bridge speeds between 10 and 30 mm/s, even if your normal print speed is 50 to 80 mm/s.

Fan speed (part cooling) is arguably the most important factor for bridging. Maximum fan speed (100 percent) is almost always recommended during bridging. The cooling fan solidifies the filament as quickly as possible, preventing it from drooping. Without adequate cooling, even short bridges will sag noticeably.

The calculator estimates the maximum reliable bridge distance using these parameters. Under ideal conditions with a 0.4 mm nozzle, 0.2 mm layer height, 20 mm/s bridge speed, and 100 percent fan, most printers can reliably bridge 40 to 60 mm. Some well-tuned machines can exceed 80 mm. The formula weights each factor and produces a conservative estimate suitable for functional prints where accuracy matters.

Material choice also affects bridging but is not included in this simplified calculator. PLA bridges the best due to its low melting point and fast solidification. PETG and ABS are more challenging. Nylon and TPU are very difficult to bridge cleanly.