Configuration • Units
Units System & Dimensional Standards
Working with US Customary, Metric SI, and Custom unit presets in LugCalc™
1. Overview of Unit Handling in LugCalc™
Dimensional consistency is paramount in structural stress analysis. In LugCalc™, unit conversion is handled transparently by a dedicated unit management engine:
- Internal Computational Standard: To prevent rounding drift during iterative optimization, the core calculation engine executes all equations in consistent base units:
- Force: Pounds-force ($\text{lbf}$)
- Length: Inches ($\text{in}$)
- Stress & Modulus: Pounds per square inch ($\text{psi}$)
- Lossless Dynamic Presentation: When you switch display units in the top bar, your stored model values are never truncated. The interface converts inputs and outputs on-the-fly to the requested display units.
2. Supported Display Unit Presets
Located on the right side of the main navigation bar, the unit segment radio selector provides three primary configurations:
Preset Force ($P$) Dimensions ($w, t, D, e$) Stress / Modulus ($F_{tu}, F_{ty}, E$) Angles ($\theta, \alpha, \beta$) US (Customary) Pounds-force ($\text{lbf}$) or Kips ($1\text{ kip} = 1{,}000\text{ lbf}$) Inches ($\text{in}$) Pounds per sq in ($\text{psi}$) or Kilopounds per sq in ($\text{ksi}$) Degrees ($^\circ$) SI (Metric) Newtons ($\text{N}$) or Kilonewtons ($\text{kN}$) Millimeters ($\text{mm}$) Megapascals ($\text{MPa} = \text{N/mm}^2$) or Gigapascals ($\text{GPa}$) Degrees ($^\circ$) Custom User selected User selected User selected Degrees ($^\circ$) Custom Display Units Mode
Clicking the "Edit" link adjacent to the unit radio buttons opens the Custom Units configuration modal. This is especially useful for multinational engineering projects where drawing dimensions are specified in millimeters ($\text{mm}$) but loads are defined in imperial pounds ($\text{lbf}$), or vice-versa.
3. Standard Engineering Conversion Factors
LugCalc uses high-precision IEEE 754 floating-point conversion factors defined by NIST standards:
Physical Quantity Imperial Unit Metric SI Unit Exact Conversion Multiplier Length $1\text{ in}$ $25.4\text{ mm}$ $1\text{ in} = 0.0254\text{ m}$ Force $1\text{ lbf}$ $4.4482216\text{ N}$ $1\text{ kN} = 224.8089\text{ lbf}$ Stress / Pressure $1\text{ psi}$ $6{,}894.757\text{ Pa}$ $1\text{ MPa} = 145.0377\text{ psi}$ Stress / Allowables $1\text{ ksi}$ $6.894757\text{ MPa}$ $1\text{ ksi} = 1{,}000\text{ psi}$ Elastic Modulus $10^6\text{ psi}\; (\text{Mpsi})$ $6.894757\text{ GPa}$ Aluminum: $\approx 10.3\text{ Mpsi} = 71.0\text{ GPa}$ 4. Non-Dimensional Design Ratios
Unit Independence: All foundational USAF efficiency charts rely exclusively on dimensionless ratios: $$e/D, \quad D/t, \quad D/W, \quad h_{avg}/D, \quad F_{ty}/F_{tu}, \quad \text{and} \quad \frac{F_{tu}}{E \cdot \varepsilon_u}$$ Because both the numerator and denominator share identical units, the resulting efficiency factors ($K_{bru}, K_{nu}, K_{tru}$) and final Margins of Safety ($MS$) are completely invariant to your chosen unit system.