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.
Belt Length Calculator
Belt length from pulley diameters and center distance.
belt length calculator pulleyChain Length Calculator
Roller chain length in links from sprocket sizes.
Pulley Calculator
Pulley speed ratio and diameter sizing.
Torque Calculator
Torque from force and lever arm, or from power and RPM.
RPM Calculator
Rotational speed from surface speed, gear ratio, or frequency.
Motor Power Calculator
Required motor power from torque, RPM, and efficiency.
motor power calculator kw hpBolts, 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 calculatorBearing 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
ISO shaft/hole fit class limits and resulting clearance.
Flow, 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.
Fluid Flow Calculator
Reynolds number and flow regime for a fluid in a pipe.
Frequently 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.