Find the Right Servo Torque for Your Robot Arm

A free browser-based servo torque calculator for robotics and automation. Enter your payload mass, lever arm length, and optional arm self-weight, then instantly see the required holding torque in kg·cm, oz·in, and N·m — with an adjustable safety margin to help you pick the right servo.

How to Use the Servo Torque Calculator

Enter the payload mass and unit

Type the mass of the object the arm will hold (grams, kg, oz or lb) and select the unit.

Enter the lever length

The lever length is the distance from the joint axis to the centre of the load (mm, cm or inches).

Add arm self-weight (optional)

If the arm itself has significant mass, enter its weight and the distance from the joint to its centre of mass.

Adjust the safety factor

Drag the slider to choose a safety margin (default 2×). The recommended servo rating is the raw torque multiplied by this factor.

Size your robot arm servo correctly — from payload and lever length to rated torque

Input Parameters

Payload Mass

Lever Length (axis to load)

Arm Self-Weight (optional)

Arm Center-of-Mass Distance (optional)

Safety Factor

1.2× 3× 2.0×

Enter payload mass and lever length to calculate the required servo torque.

Servo Database & Fit Check

Pick a servo to compare

Select a servo and compute a torque above to see whether it fits.

Torque values are rated torque at ~6 V (approx) from typical datasheets. Always confirm against your servo's own datasheet and supply voltage.

Quick Presets

Formula Reference

T = g × ( m_payload × L_payload + m_arm × L_CoM )
T_multi = g × ( Σ m_i·d_CoM,i + m_payload·L_reach )
T_rec = T × safety_factor

g = 9.80665 m/s² | 1 kg·cm = 0.0980665 N·m | 1 N·m = 141.612 oz·in

Features

Calculates holding torque from payload mass, lever length and arm self-weight Results in three units: kg·cm, oz·in and N·m — with automatic conversion Adjustable safety factor (1.2× – 3×) gives the recommended servo rating Four presets: micro gripper, 6-DOF arm segment, mid-size arm, pan-tilt camera Inputs saved to browser storage — pick up where you left off

Frequently Asked Questions

What is holding torque?

Holding torque is the torque a servo must produce to keep a load stationary against gravity. It equals mass × gravitational acceleration × lever arm length (T = m × g × L).

Why do I need a safety factor?

Dynamic loads, acceleration, friction and manufacturing tolerances all increase the real-world demand beyond the static calculation. A safety factor of 2× is a common starting point; increase it for fast or heavy arms.

What units does this calculator use?

Results are shown in kg·cm (common hobby servo datasheets), oz·in (US datasheets), and N·m (SI). The conversion is: 1 kg·cm = 0.0980665 N·m = 13.887 oz·in.

Does this work for multi-joint arms?

Calculate each joint separately. For joint N, the payload includes all the links and end-effectors further along the arm. Each joint has its own lever length.

What is the center of mass distance?

The center of mass (CoM) distance is how far the arm's own center of gravity sits from the joint axis. For a uniform rod it is half the rod length.

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Published 18 May 2026 Updated 21 May 2026