Stress Calculator
Compute normal stress from an applied force and cross-sectional area.
Formula
σ = F / A
Inputs
- Force (N)
- Cross-sectional area (mm²)
What it does
Normal stress is the force spread over the cross-section that carries it: σ = F / A.
Where it's used
Checking rods, bolts, columns and brackets under tension or compression.
How to use it
- Enter the force in newtons.
- Enter the cross-sectional area in mm².
- Compare the stress with the material’s strength.
The formula explained
- σ
- stress, MPa (= N/mm²)
- F
- axial force, N
- A
- cross-sectional area, mm²
Worked example
20 kN on a 10 mm diameter rod (area ≈ 78.5 mm²).
Inputs:
- Force: 20000 N
- Cross-sectional area: 78.5 mm²
The calculator gives:
- Result: 254.78 MPa
Tips and common mistakes
- 1 N/mm² = 1 MPa.
- Compare with the yield strength using a safety factor (mild steel yields at roughly 250 MPa).
- Holes and notches raise the local stress well above F / A.
Questions people ask
How do I find the area of a round bar?
A = π × d² / 4. A 10 mm rod has 78.5 mm²; doubling the diameter gives four times the area and a quarter of the stress.
Is 255 MPa safe for a steel rod?
No — that is about the yield strength of mild steel, so the rod would start to stretch permanently. With a safety factor of 2 the stress should stay below about 125 MPa, which needs a rod at least 14.3 mm across for 20 kN.
Is compression the same as tension?
The stress is calculated the same way, but long slender parts in compression can buckle sideways well below that stress. Columns and struts need a separate buckling check (Euler’s formula).
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Enter your values to get the result with the formula, substituted values and an explanation of each step.