Volumetric flow rate calculator (mm³/s)

What this is for: find out how many cubic millimetres of polymer per second you are demanding from your hotend at a given layer height, extrusion width and speed. It is the single number that decides whether a fast profile stands any chance of printing. The calculator runs in your browser; nothing is sent anywhere.

Speed in mm/s tells you nothing on its own. A hundred millimetres per second at a 0.12 mm layer is a stroll, while the same hundred at a 0.32 mm layer and a wide path can choke the hotend. The measure of the load is volumetric flow rate, usually shortened to flow, quoted in mm³/s. Every hotend has its ceiling — above it, it cannot melt polymer as fast as the extruder pushes it in.

How we calculate it — the formula

The basic form is trivial: flow = layer height × extrusion width × speed. Height and width in millimetres, speed in mm/s, result in mm³/s. In this simplification the path extruded by the nozzle is a cuboid of cross-section h × w, and the printer produces it at speed v.

Slicers, however, calculate it slightly more precisely. The path does not have sharp edges — its sides are rounded to a radius equal to half the layer height. The cross-sectional area is then w × h - h² × (1 - pi/4), that is roughly w × h - 0.2146 × h². For a 0.20 mm layer and a width of 0.45 mm that gives 0.0814 mm² instead of 0.0900 mm², which is 9.5% less. The calculator shows both values: the simpler one so you can work it out in your head, and the more precise one so it agrees with what your slicer reports.

Two derived results come from rearranging the same formula. Maximum speed = limit / (h × w). Maximum layer height = limit / (w × v). Both are useful when you want to speed a print up without losing quality.

A worked example with real numbers

You are setting up a fast profile: 0.4 mm nozzle, extrusion width 0.45 mm, layer 0.20 mm, infill speed 150 mm/s. Your hotend is a standard design for which you measured a limit of 10 mm³/s with PLA.

• Flow in the rectangular model: 0.20 × 0.45 × 150 = 13.50 mm³/s
• Flow in the rounded-sides model: 0.0814 × 150 = 12.21 mm³/s
• Limit used: 135% — too much
• Speed that stays within the limit: 10 / (0.20 × 0.45) = 111 mm/s
• Or, if you want to stay at 150 mm/s: drop the layer to 10 / (0.45 × 150) = 0.148 mm

So you have three ways out and all of them are calculable: slow down to 111 mm/s, drop the layer to 0.15 mm, or raise the hotend limit — that is, fit a high-flow hotend or raise the nozzle temperature within the range given by the material manufacturer.

Why exceeding the limit causes under-extrusion

A hotend is a heat exchanger of finite power. Filament goes in cold, passes through the melt zone and comes out as a melt of the right viscosity. If you push it in faster than the heater can transfer heat, the core of the strand does not fully melt. Pressure in the nozzle rises, the extruder motor starts skipping steps or the drive wheel starts to grind the filament, and less material leaves the nozzle than the slicer planned.

The symptoms look exactly like classic under-extrusion: thinner and broken walls, gaps between paths, weak top layers, poorer infill. What is distinctive is that the problem appears only on the fast sections — infill and long straight walls — and disappears on perimeters and detail, where the printer slows down anyway. If you see that pattern, it is not a blocked nozzle or moisture but an exceeded flow limit.

Temperature moves the limit up: hotter polymer is thinner and takes up heat faster. That is why fast profiles use the upper part of the manufacturer's range rather than the middle. You will find Porima's ranges in the temperature chart — PLA 200–230 °C, PETG 240–260 °C, HT PETG 270–300 °C.

What your hotend's limit actually is

Hotend manufacturers quote different numbers, measured by different methods and usually for PLA under the best conditions. The table below is orientation, not specification — it is not Porima's data, nor that of any particular printer manufacturer. Treat it as a starting point before your own measurement.

Configuration	Indicative order of magnitude
Classic short-melt-zone hotend, 0.4 mm nozzle	approx. 8–12 mm³/s
Classic hotend, 0.6 mm nozzle	approx. 12–18 mm³/s
Extended-melt-zone hotend, 0.4–0.6 mm nozzle	approx. 18–25 mm³/s
New-generation high-flow hotend, 0.4–0.6 mm nozzle	approx. 25–35 mm³/s and above

Indicative values, gathered from hotend manufacturers' declarations and workshop practice, for PLA. These are not filament manufacturer data. Measure your own hotend using the procedure below — it takes a quarter of an hour and gives a number that genuinely describes your printer.

Which Porima materials take high flow

Porima's FDM parameter table has a print speed field with three classes. It is not a limit in mm³/s — the manufacturer does not give such a number and we are not going to invent one — but it is a clear indication of where it is worth stopping.

Porima speed class	Materials	Practical conclusion
High	PLA, Tough PLA, Hyper PLA, PLA Premium, PLA Army, PLA Stone, PLA Star, PLA Pastel, Smart PLA, Eco PLA, PLA/CF, PETG, PETG Transparent, ABS, Eco ABS, ASA, PA (nylon), HIPS, Easy Flex	The hotend limits you, not the material. Worth measuring the limit and printing at 80% of it.
Medium	HT PETG, PC/ABS, ABS/CF, Silk PLA, PLA Wood	Leave a bigger margin. With Silk PLA and PLA Wood, fast flow also spoils the surface appearance.
Low	TPU Flex 98A	Flexible material buckles in the extruder under high pressure. A direct drive extruder and markedly lower speeds are recommended.

Source: Porima's official FDM parameter table, the "print speed" field. The conclusion column is our own commentary. Full listing: print temperature chart.

A separate note on path width: Porima gives a recommended nozzle diameter for each material and for most of them it is 0.4 mm, but PLA Wood and PLA Star require 0.6 mm (as does PLA Premium in the granite version). A bigger nozzle means a wider path, and a wider path means proportionally more flow at the same speed. If you move to 0.6 mm, recalculate the profile from scratch — at a width of 0.68 mm and a 0.3 mm layer you will pass 10 mm³/s at just 49 mm/s.

Frequently asked questions

What extrusion width do I enter if the slicer does not show it?

Assume 1.0 to 1.2 times the nozzle diameter — for a 0.4 mm nozzle that is 0.40–0.48 mm. That is the convention slicers apply by default. If you want it exactly, in PrusaSlicer and OrcaSlicer the value is shown directly in the extrusion settings, and in Cura under Line Width.

Does the limit apply to the whole print or only to infill?

It applies to each path separately. The highest flow usually occurs on infill and on large-area bottom layers, because that is where the printer moves fastest and the path is often widest. Perimeters and detail are safe, which is why the problem shows up selectively.

My slicer has a flow limiting option — should I use it instead of calculating?

Yes, and it is the best solution. In PrusaSlicer and OrcaSlicer the parameter is called Max volumetric speed; in Cura you have to achieve it by limiting speed. Enter your measured limit there and the slicer will slow down where needed instead of ruining the print. The calculator then serves to check how much that limit will slow the print down.

Does raising the temperature always let you print faster?

Only within the manufacturer's range. Above the upper limit you will get scorching, increased stringing and degradation of the polymer.

Related tools and pages

• 3D print parameters — the nozzle, bed and speed ranges that determine real-world flow.
• Under-extrusion — the full list of causes of under-extrusion, exceeded flow included.
• Filament grinding — the first symptom of an extruder that cannot keep up with the demanded flow.
• Weak infill — infill is printed fastest, so it falls apart first.
• Blocked nozzle — gives similar symptoms, but independently of speed.
• Layer separation — too much flow at too low a temperature weakens layer bonding.
• 3D print cost calculator — check how much you really save by printing faster.
• Print temperature chart — Porima's official parameters for 25 materials.