3D Printing Calculators
Stepper Motor Vref Calculator
https://www.3dsizing.com/calculators/stepper-vref/
Estimate only — not firmware, a slicer profile or a shop quote. Confirm on a test print.
Stepper Motor Vref Calculator
Set the tiny potentiometer from a number, not from “a bit more than the last printer”. Hobby formulas differ between legacy A4988/DRV8825 and UART TMC chips. Measure Vref on the probe pad with the driver powered.
Inputs
Results
- Vref
- 0.311V
- Peak current
- 1.131A
DC voltage from GND to the Vref pad/pot wiper.
I_rms × √2 for TMC; I_rms for A4988/DRV8825 in this hobby mapping.
Calculation method
For A4988 and DRV8825, Vref = I_rms × 8 × R_sense, treating trip current as RMS for this hobby formula, and peak current is reported as that same I_rms. For TMC2208 and TMC2209, datasheet I_rms = Vref / (R_sense × 2.5 × √2), so Vref = I_rms × R_sense × 2.5 × √2, and peak current is I_rms × √2. Sense resistance is ohms; current is amperes; Vref is volts. None of these fields convert with the imperial toggle.
Exact formula
A4988/DRV8825: Vref = I_rms × 8 × R_sense (I_trip ≈ I_rms). TMC2208/TMC2209: Vref = I_rms × R_sense × 2.5 × √2, from I_rms = Vref / (R_sense × 2.5 × √2). Peak = I_rms × √2 on TMC, I_rms on A4988/DRV8825. Limits: Confirm R_sense on the silkscreen. This is not UART milliamps. A4988 I_trip ≈ I_rms is an approximation.
StealthChop vs torque
TMC in stealth mode can stall at high speed even when Vref is “correct”. Raise current or use spreadCycle for fast travel.
Frequently asked questions
Klipper already has run_current.
If you drive TMC over UART, ignore this pot math and set run_current in amps. This page is for standalone / silent-stepstick pots.
My motor is 1.5 A rated.
Start around 0.8–1.1 A RMS unless the motor stays cool and you need the torque. Heat is the limit, not the label.
A4988 vs DRV8825 — same formula?
In this tool yes. Real A4988 current also depends on 100% chopping; treat Vref as a starting voltage and measure coil current if you can.
Where do I probe Vref?
Ground clip on a GND pin, probe on the pot wiper or labelled VREF pad. Drivers must be powered. Do not short the neighbouring pins.
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