What is bridging in 3D printing?

Bridging is when the printer extrudes filament across open air between two support points, like a bridge. The filament is pulled taut between the two sides, relying on tension and rapid cooling to hold shape.

What speed should I print bridges at?

Bridging speed should typically be 15-25 mm/s. Slower speeds allow more cooling but may cause blobs at the start. Faster speeds stretch the filament more but keep it taut. Most slicers have a dedicated bridge speed setting.

How much sag is normal for bridges?

Short bridges (under 20mm) typically have less than 0.5mm sag with PLA and good cooling. Longer bridges sag more — a 50mm bridge might sag 1-2mm. Sag increases roughly with the square of the bridge length.

Does fan speed matter for bridging?

Fan speed is critical for bridging. Maximum cooling (100% fan) helps solidify the filament before it sags. PLA bridges well at 100% fan, while ABS bridges poorly because it needs low fan speed to avoid cracking.

3DPrintCalcs

Bridge Calculator — Maximum Bridging Distance

Determine the maximum bridging distance for your printer and material settings.

Bridge Length

Unsupported span between two anchor points; spans over ~50mm usually need supports

Nozzle Diameter

A wider nozzle (0.6-0.8mm) lays a stiffer strand that sags less and spans further

Bridge Speed

Dedicated bridge print speed; 15-25 mm/s gives taut, well-cooled bridges

Cooling Fan

Part-cooling fan during bridges; 100% for PLA/PETG, low or 0% for ABS to avoid cracking

MaterialSelect the material type

How We Calculate This

Bridge Calculation

Max bridge = Material base x Cooling factor x Speed factor x Nozzle factor
Sag estimate = Length² x Material factor / (Cooling x Nozzle factor)
Bridge time = Bridge length / Print speed

The material base is a conservative, printer-dependent starting estimate (PLA ~50mm, PETG ~40mm, ABS ~25mm with a 0.4mm nozzle). Full cooling (fan factor 1.0) and a slow 15-25 mm/s speed extend the achievable span; a wider 0.6-0.8mm nozzle helps further by laying a stiffer strand. The sag estimate is a rough indicator, not a calibrated physics model — sag grows with the square of the span, so doubling the bridge length roughly quadruples the sag, while strong cooling and a thicker strand reduce it.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always verify settings with test prints before committing to final prints.