---
title: "How do I calculate the required load capacity and safety factor?"
url: "https://zimm.com/wiki/how-do-i-calculate-the-required-load-capacity-and-safety-factor/"
datePublished: "2025-11-26T11:32:21+00:00"
dateModified: "2026-05-21T09:23:12+00:00"
author: Jonathan Mildner
lang: en
canonical: "https://zimm.com/wiki/how-do-i-calculate-the-required-load-capacity-and-safety-factor/"
markdown: "https://zimm.com/ai/wiki/how-do-i-calculate-the-required-load-capacity-and-safety-factor.md"
categories: "Questions and answers about our products, Screw jacks"
---

## The basis of every safe and reliable drive design.

Correctly determining the load capacity and applying appropriate safety factors are the first and most important steps when selecting a screw jack. Underestimating the load or neglecting safety reserves can lead to overload, premature wear and, in the worst case, failure of the system.

### Step 1: Determining the maximum operating load

Identify and quantify all forces acting on the gearbox. Distinguish between:

- Static load: Force at standstill (holding force).
- Dynamic load: Force required to move the load – including friction, accelerations and, where applicable, process forces.

**Notes:** In many applications, the dynamic load is higher than the static load. For multiple gearboxes acting on one load, the load distribution must be checked; in case of doubt, design on the basis of the most highly loaded axis.

### Step 2: Applying the safety factors

Safety factors create reserves for scatter, environmental influences and short-term load peaks. Recommendation (minimum values):

- Static load: +30% safety margin
- Dynamic load: +10% safety margin

The selected screw jack must have static and dynamic load capacities that are at least equal to the design loads calculated in this way.

Example

- Holding: 7.0 kN
- Moving (incl. friction): 7.5 kN
- Design static: 7,0 kN × 1,30 = 9,1 kN
- Design dynamic: 7,5 kN × 1,10 = 8,25 kN
- Selection: Select a screw jack with permissible static load capacity ≥ 9.1 kN and permissible dynamic load capacity ≥ 8.25 kN. A gearbox with a rated load of 10 kN is suitable in this example.

### Step 3: Taking buckling load into account

For long screws under compressive load, the buckling load is often the limiting factor – not the rated load of the gearbox. Therefore, always carry out a separate buckling check for the screw. **Recommendation:** Safety factor against buckling 3–6, depending on end conditions and application.

### Short conclusion

- Fully determine static and dynamic loads.
- Add safety margins (+30% static, +10% dynamic).
- Select the gearbox on the basis of the design loads.
- Perform a separate buckling verification for the screw.

This ensures a robust, safe and long-lasting design – without unnecessary complexity.