Engineering & construction
517 engineering and construction calculators: electrical circuits, mechanics, materials, structures and building quantities. Results with the formula and units in view, so you can check a design before you build it, free in your browser.
Resistive attenuator pad calculator
A 6 dB pi pad for a 50 Ω system cuts the voltage by a factor of about 2 using two equal shunt resistors and one series resistor, with every value labeled by its…
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Return loss to SWR calculator for antenna tuning
Turn an antenna analyzer reading into SWR without logarithms: a return loss of 20 dB means a reflection coefficient of 0.1 and an SWR of about 1.2.
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Transverse shear stress calculator
Find the shear stress at a chosen fibre of a beam: a shear force of 1000 with a first moment of 20, an inertia of 40 and a width of 5 gives 100.
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Cantilever UDL moment calculator
A cantilever 4 m long under 10 N per metre carries 40 N in total and a fixed-end moment of 80 N·m, the largest bending moment in the beam.
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Parallel-axis theorem inertia calculator
Shift a section's moment of inertia to a new parallel axis: 200 about the centroid, with an area of 50 and an offset of 4, becomes 1000, because the transfer…
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Corrected endurance limit calculator
A machined 32 mm shaft in bending, with a 345 MPa baseline and 690 MPa tensile strength, keeps a corrected endurance limit of about 235 MPa.
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Principal stress 2D calculator
Turn three plane-stress readings into their extremes: normal stresses of 80 and 20 with a shear of 30 give principal stresses centred on 50, the larger one at…
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Brinell hardness number calculator
A 3000 kgf load on a 10 mm ball that leaves a 3.4 mm impression gives about 320.583 HBW. Enter the load in kgf, N or lbf to see the depth, the contact area and…
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Percent reduction of area calculator
Measure how much a tensile bar necked before it broke: an original area of 100 that shrinks to 60 at the fracture gives a reduction of area of 40 %.
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Colebrook friction factor calculator
For a relative roughness of 0.0002 at a Reynolds number of 100000, the Colebrook equation gives a Darcy friction factor of 0.019005435222 after 4 iterations.
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Orifice discharge calculator
Find how much liquid passes through a sharp-edged opening: 0.01 m² with a coefficient of 0.61 under 2 m of head lets through about 0.0382 m³/s.
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Cylindrical pipe conduction calculator
A 10 m pipe with conductivity 45 W/m·K, radii of 0.05 and 0.06 m and an 80 °C drop across the wall passes over a million watts.
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Gear output torque calculator
An input torque of 50 N·m through a 4:1 reduction becomes 200 N·m at the driven shaft, while speed drops to 0.25 of the input.
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Conductive heat flux calculator
A wall 0.2 m thick with a conductivity of 0.8 W/m·K and a 25 K difference across it conducts 100 W/m².
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Overall heat transfer coefficient calculator
Get the U-value of a wall from its layers and air films: 0.2 m of brick with films of 10 and 25 W/(m²·K) comes to just under two and a half W/(m²·K).
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Power screw efficiency calculator
See how much of your effort a square-thread screw turns into lift: a 5° lead angle with a friction coefficient of 0.15 gives an efficiency of just over a third…
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Helical spring rate calculator
Find how stiff a compression spring is: 0.002 m wire wound to a 0.016 m mean diameter with 8 active coils, in steel of eighty gigapascals, gives 4882.8125 N/m.
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Area by double meridian distance
Courses with latitudes 0, 30 and −30 and departures 40, 0 and −40 enclose an area of 600, laid out row by row like a surveying computation sheet.
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Horizontal curve long chord calculator
A curve with a 300 m radius and a 60-degree deflection has a long chord of exactly 300 m between the start and the end of the curve.
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Power factor correction kVAR calculator
Find the capacitor bank that lifts your power factor: raising 100 kW from 0.80 to 0.95 takes about 42.13 kvar, and apparent power falls from 125 kVA to about…
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Motor efficiency calculator
Find what share of electrical power a motor turns into shaft power: 800 W out of 1000 W drawn is 80 % efficiency, with 200 W lost.
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Net torque calculator
Set every turning effect about a pivot against the others: clockwise torques adding up to 20 N·m against 25 N·m the other way leave 5 N·m counterclockwise.
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Gravity neutral point calculator
Two masses of 36 and 4, placed 10 units apart, cancel each other's pull 7.5 units from the heavier one and 2.5 from the lighter one.
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Pendulum frequency calculator
A 1 m pendulum under standard gravity swings about 0.5 times per second, roughly once every two seconds, and this calculator gives the exact hertz with period…
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Principle of moments calculator
Hide one of the four values and get it back: 10 N at 1 m on one side balances a force of 20 N placed 0.5 m from the pivot on the other, both moments 10 N·m.
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Force equilibrium checker
Three forces of (10, 0), (−6, 8) and (−4, −8) add up to zero, so the set is in equilibrium. Enter each load as x and y components and get a clear yes or no…
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Bandwidth calculator
Enter a file size and a connection speed to see how long a download, upload or backup takes: 1.5 GB at 100 Mbps needs 2 minutes under ideal conditions.
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Battery size calculator
Multiply a device's power draw by the hours it must run to get the battery capacity it needs: 25 W for 8 hours calls for 200 Wh of delivered energy.
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Baud rate calculator
Divide the bit rate by the bits each symbol carries to get the symbol rate in baud: 9,600 bit/s at 2 bits per symbol is 4,800 baud.
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Battery capacity calculator
Divide a battery's amp-hour rating by the current your device draws to estimate how long it runs: a 100 Ah bank feeding a 5 A load lasts 20 hours.
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Coaxial cable impedance calculator
A coax with a 10 mm shield bore, a 2.3 mm centre conductor and a dielectric constant of 2.1 comes out at 60.850366 Ω.
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Crosstalk calculator
A 3.3 V signal 0.05 m from a neighbouring cable, with a coupling factor of 0.0002, induces 0.0132 V on it, about -47.96 dB.
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Duty cycle calculator
A 2 ms pulse in a 10 ms period is a 20 % duty cycle, with 8 ms off. Enter both times in the same unit, with no voltage needed; a pulse wider than its period is…
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LM317 calculator
With 240 Ω and 720 Ω, an LM317 delivers 5.036 V, a little over 5 V: enter the two programming resistors and get the output voltage the datasheet formula gives…
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Op-amp gain calculator
Rin of 10 kΩ and Rf of 100 kΩ give an inverting op-amp stage a gain of −10, or 20 dB. Enter the two resistors to get the signed closed-loop gain and its size in…
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PCB trace current calculator
A 10 mil outer trace in 1 oz copper with a 10 °C rise carries a little under 1 A. Enter width, copper weight and allowed temperature rise to get the IPC-2221…
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PCB trace width calculator
One ampere on 1 oz outer copper with a 10 °C rise needs a trace just under 12 mils wide. Enter the current, copper weight and heating you accept to get the…
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AC BTU for room size
A 200 sq ft room with an 8 ft ceiling and average sun needs 4,000 BTU per hour, about a small bedroom window unit.
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Aluminum weight calculator
A bar 1 m long, 0.1 m wide and 0.01 m thick at 2700 kg/m³ weighs 2.7 kg. Enter the three sizes in metres and your alloy's density, such as 7075 at 2810, to plan…
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Miter saw angle calculator
A square 90-degree corner needs 45 on the saw table and 45 on the blade; a 135-degree bay needs 22.5 and 67.5.
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Circular arch calculator
An arch spanning 8 on a radius of 5 rises 2 at the crown, with a soffit arc of about 9.273 and a chord of 8, in whatever unit you use.
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Asphalt calculator
A lane 10 m long and 4 m wide with a 0.05 m compacted lift holds 2 m³ of asphalt, or 4.8 tonnes at 2.4 t/m³.
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Birdsmouth cut calculator
A 5.5-deep rafter at a 6/12 pitch on a 3.5-wide plate needs a seat length of 3.9131 and a cut depth of 1.5652, leaving 3.9348 of stock.
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Beam load calculator
A simply supported 4 m span under 10 kN/m carries 40 kN in total, with a 20 kN·m peak moment at midspan and 20 kN of peak shear at each support.
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Board foot calculator
A board 1 inch thick, 6 inches wide and 8 feet long is 4 board feet, or 576 cubic inches at 144 per board foot.
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Board-on-board fence calculator
A 100-unit fence run with 6-unit boards overlapping by 1 covers 5 units per board, so you need exactly 20 boards.
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Boiler size calculator
A 100 m² home with 2.4 m ceilings and average insulation has 240 m³ to heat at 80 W/m³, which is 19.2 kW, so a 20 kW boiler is the shortlist.
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Bolt circle calculator
Four holes on a 100 bolt circle centred at the origin, starting at 0°, land at (50, 0), (0, 50), (−50, 0) and (0, −50), 90° apart.
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Bolt tightening torque
An M10 bolt with friction 0.14 and a 20,000 N clamp load needs a few tens of newton-metres of torque, with a nut factor inside the usual 0.16–0.22 band.
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Bowl segment calculator
A bowl of radius 10 cm filled 4 cm deep holds 416π/3 cm³, with a liquid surface of rim radius 8 cm, shown in litres and US gallons as well.
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Cement calculator
A 4 × 3 m slab 100 mm thick at a 1:2:4 mix needs 8 bags of cement, 400 kg in all. Enter your pour and the mix to know the whole bags to buy for a patio, shed…
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CFM calculator
A 20 by 15 foot room with an 8 foot ceiling and 6 air changes per hour needs 240 CFM. Enter your room and the air changes you want to pick a fan that is neither…
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Concrete block fill calculator
One hundred 16 by 8 by 8 inch two-core blocks take about 1.226 cubic yards of grout. Enter your block count and size to order fill for a grouted wall, pilaster…
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Concrete tube calculator
A 12 inch tube form poured 4 feet deep holds just over 3 cubic feet of concrete: 6 bags of 80 lb. Enter the inside diameter and the pour height before the…
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Concrete weight calculator
Two cubic feet of concrete at 150 pounds per cubic foot weigh 300 pounds. Enter the volume and the density from your mix ticket or lab test to know what a…
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Decking calculator
A 12 by 10 foot deck with 5.5 inch boards and a 1/8 inch gap takes 22 boards, 264 linear feet in all.
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Drywall calculator
A 5 by 4 m room with 2.4 m walls has 43.2 m² to board: 15 sheets of 2.4 × 1.2 m. List every wall run, closets included, and get a whole-sheet count before the…
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Elevation grade calculator
A rise of 1 over a run of 12 is an 8.333 % grade, an angle of about 4.76 degrees: the classic wheelchair-ramp slope.
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Fence estimate calculator
A 100 foot run, 6 feet high with posts every 8 feet, takes 14 posts, 39 rails and 301 pickets. Add the prices the lumber yard gave you and get the material list…
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Fence post burial depth
An 8 ft post where frost reaches 4 ft must go 4 ft deep and leaves 4 ft above ground. The hole is one third of the post or the frost line, whichever is deeper…
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