Factor of Safety Calculator

Created by Luis Hoyos
Last updated: Nov 05, 2022

If you're wondering how to calculate the safety factor, you're in the right place. This calculator uses the safety factor equation to determine how safe a structure is.

Input the maximum load your structure can support (maximum strength) and the one you expect it to support (design load), and the calculator will use the safety factor formula to give the result. If you've already established a design safety factor and know the maximum strength, you can also input those two variables and calculate the load your design must support.

What is the factor of safety?

In engineering, the factor of safety (FoS), also known as the safety factor (SF), is the ratio of the strength of a component or system to the loads it needs to support. We can use the safety factor for various purposes:

  • Indicate the margin by which a system could fail.
    • For example, a safety factor of 2 means that the system can support twice the loads we expect it'll experience.
    • If we designed a car and calculated the factor of safety to be 3, we hope it can safely withstand three times the loads we expect it to experience.
  • Indicate reliability or robustness. A higher safety factor indicates more tolerance to error and less likelihood of failure.

🔎 Are you craving more knowledge about the safety of cars? Perhaps you'll find our car crash calculator interesting.

The design factor we choose will mainly depend on two things:

  1. The consequences of the failure.
  2. The accuracy with which we can predict the loads.

For example, suppose we're designing a wrench to apply a bolt torque to threaded fasteners. In that case, the consequences of using a torque that exceeds the strength of the wrench material could be simply damaging it and having to replace it with another wrench.

On the other side, if you're designing a pressure vessel and the stress caused by the pressure inside it surpasses the strength of the vessel material, the consequences include the death of many people.

Paradoxically, the accuracy of the predictions could be in favor of the more dangerous system. We can calculate the stress the pressure vessel will suffer (with a hoop stress calculator), but we cannot precisely predict how a user will use a wrench.

Now that we know its importance, let's look at how to find the factor of safety.

How to calculate the factor of safety - Formula

As it is the ratio of the strength system to the loads it needs to support, we calculate the factor of safety with the equation:

Factor of safety = Maximum strength / Design load

And that's how you find the factor of safety! Although this calculator focuses on forces, we can also calculate the factor of safety using stresses:

Factor of safety = Maximum stress / Design stress

Luis Hoyos
Maximum strength
Design load
Factor of Safety
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