Stepper Motor Current Calculator

Calculate the correct Vref and current settings for your stepper motor drivers.

Stepper Driver

Motor Rated Current *required

Found on motor datasheet or label

Current Percentage

70-90% recommended to reduce heat

Common Motors

Driver Settings

Vref Setting

0.00 V

Motor Rated Current 0 A

Percentage Used 0%

Run Current (Peak) 0 A

RMS Current 0 A

Formula Used —

Configuration

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Understanding Stepper Motor Current

Setting the correct current for your stepper motors is crucial for optimal performance. Too low and your motors will skip steps; too high and they'll overheat and potentially damage themselves or the drivers.

Peak vs RMS Current

Motors are typically rated for peak current, but stepper drivers often use RMS (Root Mean Square) current. The relationship is:

RMS Current = Peak Current ÷ √2 (≈ 0.707 × Peak)

This is why we recommend running at 70-90% of rated current—it accounts for this conversion and adds a safety margin.

Vref Explained

Vref is the reference voltage used by analog drivers (A4988, DRV8825) to set current. You measure it at a test point on the driver with a multimeter. Each driver has a different formula to convert Vref to current.

TMC Drivers (2208, 2209, 2130, 5160)

TMC drivers can be configured via UART or SPI, making Vref adjustment less common. For these drivers, you typically set the current directly in firmware (Marlin, Klipper, RRF) in milliamps.

Driver-Specific Formulas

A4988: Vref = Current × 8 × Rs (Rs typically 0.1Ω)
DRV8825: Vref = Current ÷ 2
TMC2208/2209: Vref = (RMS × 1.41) ÷ 1.77
TMC2130/5160: Set run_current in firmware (mA)

Frequently Asked Questions

How do I find my motor's rated current?

Check the motor's label or datasheet. It's usually listed as "Rated Current" or "Phase Current" in amps. Common NEMA 17 motors are rated 1.0-2.0A. If you can't find it, search the motor's model number online.

Why are my motors getting hot?

Stepper motors do get warm during operation—up to 60°C (140°F) is normal. If they're too hot to touch for more than a second, reduce the current. TMC drivers in StealthChop mode run cooler than SpreadCycle.

My motors are skipping steps. Should I increase current?

Possibly, but first check: Are belts tight? Are pulleys secure on shafts? Is acceleration too high? Is there mechanical binding? Only increase current if these are ruled out, and don't exceed 100% of rated current.

What current should I use for different axes?

X and Y axes typically need the most current (80-100% rated) for fast movements. Z axis can often run lower (60-80%) since it moves slowly. Extruder depends on your setup—direct drive needs less than Bowden.

How do I measure Vref?

With power on but motors disabled, touch your multimeter's positive probe to the Vref potentiometer or test point (small metal pad on the driver) and negative to ground. Adjust the potentiometer to set the desired voltage.