Holding torque scales by an order of magnitude across the three common NEMA frame sizes: roughly 0.2–0.8 Nm for NEMA 17, 1–3 Nm for NEMA 23, and 4 Nm and above for NEMA 34 [S3]. The number on the nameplate is the faceplate width in tenths of an inch, not a torque rating, which is why two NEMA 17 motors from different vendors can sit at 0.28 Nm or 0.65 Nm depending on body length [S4].
Selecting between them is a mechanical-engineering problem, not a catalogue one. The faceplate decides mounting compatibility, the stack length sets torque, and the winding decides whether a stepper drive can run that frame at the speed the application actually needs [S1].
Holding torque ranges and what the numbers actually cover
Published ranges for the three common NEMA sizes cluster tightly when cross-checked. NEMA 17 lands at 0.2–0.8 Nm, equivalent to roughly 30–80 N·cm or 28–113 oz·in [S1][S3]. NEMA 23 sits at 0.5–2.0 Nm in vendor cross-reference tables and 1–3 Nm in selection guides, with a 76.5 mm stack example delivering 2.00 Nm at 2.8 A [S7][S8]. NEMA 34 begins above 2.0 Nm and is consistently listed in the 4–12 Nm band once stack length is extended [S3][S8].
The wide spread inside each frame comes from stack length, not from the NEMA standard itself. A pancake NEMA 17 (25–30 mm body) typically delivers one-third the holding torque of a long-body NEMA 17 (55–60 mm body) on the same winding platform [S4]. For thermal planning, the rule of thumb that follows is that doubling torque roughly doubles rotor mass and copper volume, which is why NEMA 34 machines need supply rails in the 60–80 V DC range to keep high-speed torque from collapsing [S1][S3].
Frame geometry, shaft, and current draw
Faceplate dimensions are 42 × 42 mm for NEMA 17, 57 × 57 mm (sometimes rounded to 58 mm by Asian vendors) for NEMA 23, and 86 × 86 mm for NEMA 34 [S2][S4]. Shaft diameters step up with frame size, 5 mm for NEMA 17, 6.35–8 mm for NEMA 23, and roughly 12.7–14 mm for NEMA 34, which dictates the coupler, pulley, and gearbox selection downstream [S1].
Rated phase current is the second lever. NEMA 17 typically draws 0.8–2.0 A from a 2–6 V coil; NEMA 23 draws 2.0–4.5 A from 3–8 V coils; NEMA 34 commonly runs 3.0–7.0 A at higher bus voltages to hold torque at speed [S1][S3]. A 1.2 A NEMA 23 example held 3.2 kg·cm (about 0.31 Nm) in one bench test, illustrating how low-current windings sacrifice torque for cooler operation [S6]. This is also where a stepper motor selection crosses into driver sizing: an undersized driver will choke a NEMA 34 in the mid-speed band even though the motor can theoretically deliver the torque.
Decision matrix: when each frame fits the job
A NEMA 17 is the right pick for 3D printers, camera sliders, lab automation, and small pick-and-place axes where the load inertia sits below roughly 100 kg·cm² and the cycle demands fast accel rather than raw holding force [S1][S3]. A NEMA 23 covers the mainstream CNC router, laser engraver, and packaging line: 1–3 Nm is enough to drive a 2005 ballscrew on a small gantry and still mill aluminium at sensible feed rates when paired with a DM542-class driver [S7]. A NEMA 34 belongs on heavy gantries, larger mills, and any axis that pushes torque above 3 Nm continuously; it also tolerates gearbox pairing better because the rotor inertia is high enough to mask gearbox cogging [S1][S3].
The crossover points to remember: 1 Nm separates the comfortable NEMA 17 ceiling from a real NEMA 23 application, 3 Nm is the practical NEMA 23 ceiling before stack length and heat become painful, and anything above 4 Nm is a NEMA 34 job in mainstream sizing [S3][S8]. Going one frame up rarely hurts performance; it hurts panel space, power supply sizing, and budget, so a 24 V bus on a NEMA 34 is a common mistake that loses the very torque the larger motor was bought for [S1].
Thermal and drive-side constraints that change the answer
Holding torque is a static number measured with the rotor stationary and the coils at room temperature. Under continuous motion, available torque falls as winding temperature rises, often by 15–25% at the rated insulation class, which is why the same NEMA 23 can feel strong on a bench and weak inside an enclosed machine [S2]. Microstepping smooths motion but does not raise torque; it redistributes it across smaller increments and can mask resonance in low-inertia loads.
Driver voltage is the most common silent failure. A 24 V supply on a 3 Nm NEMA 23 will deliver the rated holding torque but surrender most of its high-speed torque, while a 48–72 V bus on the same motor can keep usable torque out to 1500 rpm or beyond [S1]. For heat-prone builds, derate the published torque by at least 20% before sizing the safety margin on acceleration, and budget for forced airflow on any NEMA 34 in a sealed cabinet.
Common failure modes and selection mistakes
Three errors show up repeatedly in retrofit projects. First, swapping a NEMA 17 for a NEMA 23 without re-checking the stepper drive current limit, which overheats the smaller driver and trips protection mid-cut [S5][S7]. Second, choosing a NEMA 17 pancake for an aluminium-mill retrofit because the faceplate fits, then losing steps the first time the spindle engages. Third, oversizing to NEMA 34 on a 24 V supply and concluding that steppers are weak, when the real problem is the bus voltage [S1].
Body length matters more than frame size for fine-tuning. A long-body NEMA 23 at 76.5 mm typically reaches 2 Nm, while a short-body NEMA 23 at 41 mm lands closer to 1 Nm, which is the same torque a long NEMA 17 can deliver at lower current draw [S4][S7]. When two motors in adjacent frame sizes overlap in torque, pick the smaller one to keep the supply, driver, and thermal budget honest.
Application fit, sourcing, and standards notes
By application, the bands line up as: 3D printers, optical benches, and small robotics take NEMA 17; CNC routers, laser engravers, and packaging pick-and-place take NEMA 23; large-format CNC, textile cutters, and heavy automation take NEMA 34 [S1][S3][S8]. Hobby CNC builders have documented an upgrade path from NEMA 17 to NEMA 23 on X-Carve-class machines, with holding torque rising from about 70 oz·in (roughly 0.49 Nm) to 140–175 oz·in (roughly 0.99–1.23 Nm) at the same current class [S5].
For thermal and electrical context on adjacent industrial components, see our motor thermal overload relay sizing notes, and for higher-level protection logic, the ANSI 27 and 46 undervoltage and unbalance functions walkthrough applies when the stepper is fed from a protected bus. No single IEC or NEMA standard pins down holding torque values, since NEMA only standardises the mechanical faceplate, so verify each motor's datasheet against the vendor's actual test conditions before locking the design [S4].
Spec-level background on the components involved: holding furnace.