Real formulas, shown
Every result shows the equation behind it — no black box.
Instant, no signup
Calculators run in your browser. No account, no email wall.
SI + Imperial
Switch units per calculator, no separate "US version" page.
One tool, one job
Each calculator is built for a single, specific calculation — done properly.
Shafts, Gears & Drives
Size shafts, gears, belts, and pulleys for a power transmission path — from motor output to driven load.
Shaft Diameter Calculator
Find minimum solid shaft diameter from torque or transmitted power.
shaft diameter calculator for torqueGear Ratio Calculator
Get gear ratio, output RPM, and output torque from tooth counts.
gear ratio calculator for rpmGear Design Calculator
Module, pitch diameter, and center distance for spur gear pairs.
gear design calculator moduleBelt Length Calculator
Belt length from pulley diameters and center distance.
belt length calculator pulleyChain Length Calculator
Roller chain length in links from sprocket sizes.
chain length calculator sprocketPulley Calculator
Pulley speed ratio, diameter sizing, and belt speed.
pulley speed ratio calculatorTorque Calculator
Torque from force and lever arm, or from power and RPM.
torque calculator force lever armRPM Calculator
Rotational speed from surface speed, or motor frequency and poles.
rpm calculator surface speedMotor Power Calculator
Required motor power from torque, RPM, and efficiency.
motor power calculator kw hpShaft Torsional Stress Calculator
Torsional shear stress in a shaft from torque and diameter.
shaft torsional stress calculatorShaft Key Size Calculator
Keyway/key size for a shaft from torque and diameter.
shaft key size calculatorGear Module Calculator
Gear module from pitch diameter and tooth count.
gear module calculatorGear Center Distance Calculator
Center distance for a gear pair from module and teeth.
gear center distance calculatorGear Pitch Diameter Calculator
Pitch diameter from module and tooth count.
gear pitch diameter calculatorMotor Torque Calculator
Motor output torque from rated power and speed.
motor torque calculator power rpmMotor Current Calculator
Full-load current from motor power, voltage, and power factor.
motor current calculatorRPM to Linear Speed Calculator
Convert rotational speed to linear surface speed.
rpm to linear speed calculatorBolts, Beams & Springs
Check fastener preload, beam deflection, spring rates, and weld strength before you commit to a design.
Bolt Torque Calculator
Tightening torque and clamp load for metric bolts.
bolt torque calculator metricBeam Deflection Calculator
Deflection and bending stress for a simply supported beam.
beam deflection calculatorSpring Design Calculator
Spring rate, deflection, and shear stress for compression springs.
spring rate calculatorWelding Calculator
Fillet weld leg size and load capacity.
fillet weld strength calculatorBolt Preload Calculator
Target preload from bolt grade, size, and proof stress.
bolt preload calculator torqueBearing Life & Precision Fits
Estimate bearing life and get the right clearance for shaft-and-hole fits.
Bearing Life Calculator
L10 bearing life from dynamic load rating and speed.
bearing life calculator L10Tolerance Stack-up Calculator
Worst-case and RSS tolerance stack-up for a dimension chain.
tolerance stack up calculatorFits & Clearances Calculator
Clearance or interference between a shaft and hole from their deviations.
shaft hole fit clearance calculatorFlow, Pressure & Heat Transfer
Size pipework, pressure vessels, and heat exchangers with standard fluid and thermal formulas.
Pipe Flow Calculator
Flow velocity, Reynolds number, and pressure drop in a pipe run.
pipe flow calculator pressure dropPressure Vessel Calculator
Minimum wall thickness for a thin-wall pressure vessel.
pressure vessel wall thickness calculatorHeat Transfer Calculator
Conductive and convective heat transfer rate.
heat transfer calculator conduction convectionFluid Flow Calculator
Reynolds number, flow regime, and flow rate for a fluid.
reynolds number calculatorThermal Expansion Calculator
Dimensional change from temperature change and material.
thermal expansion calculator coefficientPump Power Calculator
Calculate hydraulic and shaft power from flow rate, head, and pump efficiency.
pump power calculator hydraulic powerPipe Pressure Drop Calculator
Calculate pressure loss through pipes and fittings from flow and pipe properties.
pipe pressure drop calculatorCutting, Feeds & Cycle Time
Estimate cutting speeds, chip loads, and machining time for turning and milling operations.
Plate, Pipe & Bar Weight
Find the weight of common stock shapes from dimensions and material density.
Steel Plate Weight Calculator
Plate weight from length, width, thickness, and density.
steel plate weight calculator kgPipe Weight Calculator
Pipe weight per unit length from OD, wall thickness, and density.
pipe weight calculator kg per meterRound Bar Weight Calculator
Round bar weight from diameter, length, and density.
round bar weight calculator kgFrequently asked questions
Are the calculators on TheMechBox free to use?
Yes. Every calculator is free, runs instantly in your browser, and doesn't require an account or email signup.
Can I use these calculators for real engineering design?
They use standard mechanical engineering formulas and are suitable for estimation, coursework, and first-pass sizing. Always verify a final design against the relevant design standard and have it checked by a qualified engineer.
Which units do the calculators use?
Most calculators support both metric (SI) and imperial units, with a unit toggle next to the relevant inputs.