Part of the CalcProMaster guides library · Electrical, mechanical & structural math
Engineering calculations punish small errors — a wrong voltage-drop figure means undersized cables, a wrong gear ratio means a drivetrain that never reaches design speed. These guides show the formula, the assumptions behind it, and a worked example you can check by hand.
Methodology: Standard engineering formulas and material properties from published handbooks, with safety factors noted where they apply.
Every engineering formula hides assumptions, and knowing them matters more than memorizing the algebra. Voltage drop = 2 × L × I × ρ ÷ A assumes a resistive load, a conductor at operating temperature, and length L counted along both conductors — hence the 2. Ignore any of these and the number is precise but wrong.
A worked check: 20 m run, 10 A load, 2.5 mm² copper (ρ ≈ 0.0175 Ω·mm²/m). Drop = 2 × 20 × 10 × 0.0175 ÷ 2.5 = 2.8 V — about 1.2% of a 230 V supply, comfortably inside the 3–5% usually tolerated. If your real circuit shows double that, the likely culprits are temperature-derated conductors or an undersized return path, not the formula.
Awg, mm², psi, bar — converting the units engineering specs mix freely.
Load-bearing material math for structural and civil work.
VD = 2 × L × I × R per conductor pair, where L is one-way cable length in metres, I the load current, and R the conductor resistance in ohms per metre. Keeping drop under 3% of supply voltage is the common design target for branch circuits.
It is driven-teeth ÷ driver-teeth: a 4:1 ratio cuts speed to a quarter while multiplying torque fourfold (minus friction losses). The gear ratio calculator converts ratio, RPM and torque in both directions.
Voltage Drop Calculator Gear Ratio Calculator Torque Calculator