Orca Slicer flow rate calibration

Flow rate calibration sets how much plastic your printer extrudes, so walls come out the right thickness and top surfaces are smooth instead of gappy or over-filled. In Orca Slicer the value you are tuning is the flow ratio, sometimes called the extrusion multiplier, where 1.0 means the nominal amount of filament. The test prints a set of small blocks at slightly different flow ratios, you pick the smoothest one, and you save that value to the filament. It is one of the first calibrations worth doing for any new filament.

What flow rate does

Flow rate controls the amount of filament pushed out per move. Too much, and the print over-extrudes: blobs, rough surfaces, stringing and parts that measure oversize. Too little, and it under-extrudes: gaps between lines, weak layers, and pinholes in the top surface. Calibrating the flow ratio brings extrusion to the right amount for that specific filament, which is the base every other quality setting builds on.

Before you start

Set the calibration up so the result is trustworthy. Pick the exact printer, filament and process you will use, because the test is based on the filament’s current flow ratio, so the correct filament has to be selected first. If your printer is a Bambu Lab machine, do not turn on its own Flow calibration option for this test, since that fights the manual one. It also helps to have basic extruder steps and the line width sorted first, because a mechanical problem or a low maximum volumetric speed can make every block look the same and hide the real flow difference.

YOLO method (recommended)

The YOLO method finds a good flow ratio in a single print, which is why it is the default choice. It adjusts the flow ratio using the formula old flow ratio plus or minus the block’s modifier.

1. Open the Calibration menu at the top of Orca Slicer and, under Flow rate, choose YOLO (Recommended).
2. A project of eleven blocks is created, each with a different flow ratio modifier. The recommended range is minus 0.05 to plus 0.05 in steps of 0.01. The Perfectionist variant uses minus 0.04 to plus 0.035 in finer steps of 0.005.
3. Slice and print the project.
4. Look at the top of each block and find the one with the smoothest, most even surface. Running a fingernail lightly across the tops helps you feel which is flattest.
5. Add that block’s modifier to your current flow ratio to get the new value. For example, a current flow ratio of 1.0 and a best block of plus 0.02 gives a new flow ratio of 1.02.
6. Enter the new flow ratio in the filament settings and save it.

Two-pass method (finer)

The older two-pass method takes longer but lets you narrow in with smaller steps, which helps with tricky filaments like silk PLA. It uses the formula old flow ratio times (100 plus the modifier) divided by 100.

1. In the Calibration menu, under Flow rate, choose Pass 1. A project of nine blocks is created, each with a different modifier.
2. Slice, print, and pick the block with the smoothest top surface.
3. Update the flow ratio with the formula. For example, an old flow ratio of 0.98 and a chosen modifier of 5 gives 0.98 times 105 divided by 100, which is 1.029.
4. Save that value, then choose Pass 2 from the same menu. This creates ten blocks that compare smaller steps around your Pass 1 result.
5. Print Pass 2, pick the smoothest block again, apply the formula once more, and save the final flow ratio.

The objective alternative

If every block looks identical to your eye, you can measure instead of judging by feel. Print a single-wall test cube, then measure the wall with calipers in a few places and average it. Divide your target wall thickness by the measured thickness and multiply by the current flow ratio. A target of 0.40 mm, a measured 0.42 mm and a current 1.0 gives a new flow ratio of about 0.95. Update the filament, reprint, and repeat until the measured wall is within a few percent of the target. This removes the guesswork when the printed blocks are too close to tell apart.

Saving and when to recalibrate

Flow ratio is saved per filament, so each spool or material can hold its own value. Recalibrate when you change to a different filament or brand, when a new spool of the same filament behaves differently, or when you change nozzle size. After finishing any calibration, start a new project to leave calibration mode before you slice a real model. From here, the precision settings fine-tune dimensional accuracy, and pellet printers tune their equivalent value on the pellet flow coefficient page.

Frequently asked questions

What is flow rate calibration in Orca Slicer?

It is a test that sets the flow ratio, the value that controls how much filament your printer extrudes. Orca Slicer prints a set of blocks at slightly different flow ratios, you pick the smoothest one, and you save that value to the filament so walls and surfaces come out clean.

Should I use YOLO or the two-pass method?

Use YOLO for most filaments, since it finds a good flow ratio in a single print. Switch to the two-pass method when you want to narrow in with smaller steps, for example on silk PLA or when YOLO gets you close but not perfect.

How do I pick the best block?

Choose the block with the smoothest, most even top surface, with no gaps between lines and no rough over-filled patches. Running a fingernail lightly across the tops helps you feel which one is flattest when they look similar.

Why do all my flow rate blocks look the same?

That usually means something else is masking the flow difference, such as a mechanical issue like a loose gantry or a maximum volumetric speed set too low. Sort those out first, or switch to the single-wall cube method and measure the wall with calipers instead of judging by eye.

Do I calibrate flow rate for every filament?

Yes, ideally. Flow ratio is saved per filament, and different materials and even different brands of the same material extrude a little differently, so calibrating each one gives the most consistent prints.