How to Calibrate Flow Rate on a 3D Printer
Contents
Even when your e-steps are right, two different brands of PLA can give different results at the same settings. Filament diameter, density and how it flows when melted vary from brand to brand. Flow rate is the fine adjustment that corrects this difference. You move the slicer's 100% value a few points up or down to suit the filament you use.
When do you need it?
- When you start using a new filament brand or type.
- When walls are thicker than they should be, edges bulge and the surface has bumps (over-extrusion).
- When walls are thin and the top surface has gaps (under-extrusion).
- When parts that should fit together sit too tight or too loose.
Before this calibration, hardware problems should be solved and e-steps should be set. Otherwise flow hides another error. If you have obvious gaps, look at the under-extrusion guide first.
Signs of over- and under-extrusion
| Sign | Over-extrusion | Under-extrusion |
|---|---|---|
| Wall thickness | Thicker than specified | Thinner than specified |
| Top surface | Bumpy, raised, nozzle marks | Gaps between lines |
| Edges | Bulging, lip forming | Sharp but full of holes |
| Parts that fit together | Tight, forced | Loose, gappy |
| Holes | Smaller than specified | Normal or larger |
Method 1: single-wall cube
This method compares the line width the slicer asks for with the width actually printed.
Preparation
- Use a 20 × 20 × 20 mm cube model.
- In the slicer make these settings:
- Wall count: 1
- Top layers: 0
- Infill: 0%
- Bottom layers: 1 or 2 (so the cube sticks to the bed)
- Set the line width to a known value, for example 0.45 mm.
- Set the flow ratio to 100%.
- If you like, use the slicer's "vase mode" (spiralize) option. This prints a single-wall cube without a seam.
Measure
- When the print is done, measure the wall thickness with calipers.
- Measure at the middle of each of the four walls, a few millimeters above the bottom. Corners and the lowest layers are misleading.
- Average the measurements.
Calculate
New flow = Current flow × Requested width ÷ Measured width
Example: current flow 100%, requested width 0.45 mm, measured average 0.48 mm. New flow = 100 × 0.45 ÷ 0.48 = 93.75%
Things to watch
- Do not squeeze the calipers' jaws too hard. A thin wall gets crushed and the measurement comes out small.
- This method needs measurements accurate to 0.01–0.02 mm. Cheap plastic calipers may not be good enough.
- The measurement is very sensitive to wall smoothness. If the result is unexpected, confirm it with the second method.
Method 2: top surface test
This method needs no calipers and directly judges the top surface of your real prints.
- Prepare small flat squares of about 30 × 30 × 3 mm.
- Print each square with a different flow ratio: for example 90%, 93%, 96%, 99%, 102%.
- Leave the top layer count normal (4–5).
- After printing, look at the top surfaces under good light and touch them with your finger.
How to judge:
- Gaps and separated lines: Flow is low.
- Smooth surface with lines fused together: Flow is right.
- Bumps, raised areas and bulging at line ends: Flow is high.
The "Calibration > Flow rate" menu in OrcaSlicer and Bambu Studio builds this test automatically. It offers a two-stage test, a coarse pass and then a fine pass.
Which value is normal?
For most filaments the right flow is between 90% and 105%. Results outside this range usually point to e-steps, filament diameter or a hardware problem.
Other flow-related settings
- First layer flow: Some slicers have a separate flow setting for the first layer. It should mostly stay at 100%. If you have an elephant's foot problem, it helps to keep it lower.
- Pressure advance / linear advance: Balances nozzle pressure during speed changes. If you see bulging at corners or thinning at the start of lines, calibrate this setting.
- Maximum volumetric flow: At speeds beyond the hotend's limit, you get under-extrusion no matter what the flow setting is.
Save the result
Save the flow value you found in the slicer profile for that filament. Put the brand and color in the profile name. Even between colors of the same brand there can be a difference of a few points.
Frequently asked questions
Should I change flow or e-steps?
E-steps belong to the hardware and are set once. Flow is a fine adjustment specific to a filament. If there is the same deviation with all filaments, change e-steps; if only one particular filament deviates, change flow.
Does flow calibration fully fix dimensional accuracy?
It improves dimensional accuracy considerably. But for exact holes and outside dimensions you may also need the slicer's "horizontal expansion" (XY compensation) settings and elephant's foot compensation.