EngCalc Help Documentation

A complete guide to the engineering calculators, from typing a value to reading the answer.

Last Updated: November 9, 2026

1. Getting Started

The tabs choose All or one of the five kinds: Structure, Building, Fluids, Electrical and Circuits. In a kind, the row of buttons under the tabs picks the calculator. All lists every calculator with a search box, and your favourites and recent calculators at the top; Find in the toolbar (or /) searches from anywhere in the tool.

Every calculator opens with example values. On a computer the boxes are on the left and the answer on the right; on a phone the answer comes under the boxes, and a one-line summary stays at the top of the screen while you type. Above the answer, the star keeps the calculator in your favourites, and Share, Copy, Print and Reset do what they say.

2. Typing Values and Units

The SI and US switch in the toolbar (or U) sets every calculator to metres, newtons and pascals or to feet, pounds and psi, and converts what you typed. Each box also has its own unit list; changing it keeps the size (6 m becomes 6000 mm). A box takes:

• a number, 12.5, with commas for thousands (1,200, 1,00,000) or a decimal comma (2,5);
• a unit after it: 25 mm, 3.5 kN, 12 kN/m, 45 psi, 2 L/s;
• feet and inches: 12'6", 6' 4 1/2", 12ft 6in; fractions: 3/8, 1 1/2 in;
• sums: 2*450 + 30, (2+3)*4, 3^2;
• the shorthand printed on parts: 4k7 (4.7 kilohms), 2R2 (2.2 ohms), 1M5, 100n, 47p, 4u7.

The line under each box shows what was understood (for example "= 3.81 m" for 12'6"), or says what could not be read. Boxes hold at most 60 characters; values beyond what an engineering calculation needs, and temperatures below absolute zero, are refused.

3. Beam Calculator

1. Type the Length of the beam.
2. Under Supports, choose how it is held: simply supported, cantilever, fixed both ends, fixed and propped, with an overhang (type the overhang), continuous (2 to 6 equal spans) or Own supports, where you add up to 12 pinned, roller or fixed supports anywhere along it.
3. Under Loads, each load is a Point load, a Spread load (along the whole beam or from one place to another), a Varying load (from one value at its start to another at its end) or a Moment. Loads are downward and moments clockwise when positive. Up to 30 loads. Tick Add the weight of the beam itself to include it (it needs the section's area).
4. Under Section and material, choose a Steel beam (ISMB 100 to 600, IS 808:1989), a Shape with its sizes, or Own values (I, Z and A); then the material (steel grades, stainless, aluminium, timber, uncracked concrete, or your own E and strength) and the Allowed sag.

The answer gives the largest bending moment and where it is, the largest shear and deflection, the bending stress, the beam's own weight, and checks: sag in each span (free ends against twice their length), bending stress against 0.66 fy (timber against its bending strength) and shear against 0.4 fy. The drawing shows the beam, its loads and supports with the reactions, and the shear, moment and deflection diagrams; point at them or use the arrow keys to read values anywhere. Save the values (CSV) writes them for a spreadsheet; the reactions table and "How it is worked out" follow.

The reactions come from beam elements with a node at every support and load, the shear and moment from balancing the forces left of each point, and the deflection from at least 800 short elements, so the results are those of an elastic beam (to within rounding, a few parts in 100,000). Concrete uses the uncracked stiffness, so a real concrete beam sags two to three times more over time. Sag limits: IS 800 span/300 or /360 for floors, IS 456 span/250 (final) or /350 (after finishes), the IBC span/360, /240 or /180. The loads are used as typed: multiply them by your code's load factors for strength. It is a check for planning and learning, not a structural design.

4. Section Properties

Choose a Shape (rectangle, box, round bar, tube, I-beam, channel, T-section, angle) and type its sizes, or a Steel beam from the ISMB list, and a material for the weight (typical densities). You get the area, the weight a metre, the centroid, Ix and Iy, the elastic section moduli at the top and bottom and both sides, the plastic moduli with the shape factor, the radii of gyration, the torsion constant (exact for round bars and tubes, Bredt's formula for boxes, a thin-walled estimate for open shapes) and, for angles and other unsymmetrical shapes, the principal moments and the smallest radius of gyration, which governs their buckling. The drawing shows the shape with its centroid. Corners are taken as sharp; the ISMB values are those of IS 808:1989 and include the fillets (IS 808:2021 has since replaced it: check the mill's table).

5. Column Buckling

1. Type the Length between supports and choose the End conditions. With Use the design value of K ticked, the larger values the codes recommend are used (0.65 for both ends fixed, 0.8, 1.0, 1.2, 2.1 for a flagpole, 2.0). Or type your own K.
2. Choose the section and whether it buckles about the weakest axis or the strong axis only, and the material.
3. Choose the Code (IS 800:2007, EN 1993-1-1, AISC 360-16 LRFD or ASD) and the Buckling curve, and type the load on the column if you want it checked.

The answer gives the design strength by the chosen code, Euler's load and the slenderness, with a chart of design stress against slenderness and a table of every code. IS 800 uses its classes a to d (imperfection factors 0.21, 0.34, 0.49, 0.76) and a partial factor of 1.10; Eurocode adds curve a0 (0.13) and uses 1.0; AISC uses 0.658 to the power fy/Fe below a slenderness of 4.71 times the root of E/fy and 0.877 Fe above it, with 0.9 for LRFD and 1.67 for ASD. Slenderness is checked against 180 for steel and aluminium (IS 800 Table 3) and 200 for other materials. Local buckling of thin plates is not checked. For timber and concrete, the design strength still uses the steel curves; use EN 1995 or IS 883, or IS 456 or ACI 318.

6. Steel Bars

Add a row for each bar mark: a name, the Diameter (6 to 40 mm), the Length of each (the cutting length from your bar bending schedule, with bends and hooks) and How many (up to 100,000). Type the length bars are sold in (12 m is usual) and choose the lap, 40, 50 or 60 times the diameter. The answer gives the total weight, the stock bars to buy and their weight, and a table by diameter with the weight a metre (d squared over 162.2), the length, the bars to buy and the offcuts. Under Bars across a slab, the width over the spacing, plus one, gives how many bars fit.

7. Metal Weight

Choose the shape (round, square or hexagon bar, flat bar or plate, round pipe, square or rectangular tube, angle, channel, I-beam), type its sizes, the length and how many, and choose the metal (typical densities from aluminium at 2,700 kg a cubic metre to lead at 11,340). With a price per kg (or per lb in US units) you get the cost; without one, the surface to paint. Rolled sections with fillets weigh a little more than their sizes give; use the table weight for standard sections.

8. Staircase

Type the floor-to-floor height (up to 30 m), the riser you would like, the tread, the stair width and the waist slab for a concrete stair, and choose the building code. The risers are the height over the riser you typed, rounded, and then kept within the code's limits. The checks:

• India NBC 2016: one- or two-family homes, riser at most 190 mm and tread at least 250 mm, width 1.0 m; flats, hostels and lodging, 150 and 300 mm, width 1.25 m; other buildings, 150 and 300 mm, width 1.5 m; at most 12 risers a flight and 2.2 m of headroom.
• US IRC (homes): riser at most 7 3/4 in, tread at least 10 in, width 36 in, headroom 6 ft 8 in, at most 151 in of rise a flight. US IBC: riser 4 to 7 in, tread 11 in, width 44 in, headroom 80 in, at most 12 ft a flight.
• UK Part K, private stair: rise 150 to 220 mm, going 220 to 300 mm, pitch at most 42 degrees, two risers plus a going between 550 and 700 mm, headroom 2.0 m.

Blondel's comfort rule (2R + T between 600 and 650 mm) is checked too. The answer gives the risers and treads, the going, the pitch, the stringer length and the concrete, with a side view to scale. When a flight has more risers or rise than the code allows, it says how many flights you need; add each landing's depth to the going.

9. Roof, Slope and Digging

• Roof pitch: type any two of rise, run and angle (or the pitch as rise in 12), the overhang measured flat and, if you like, the roof area seen from above. You get the angle, the pitch, the rafter length with the overhang, the slope and the true area of the roof (the plan area over the cosine of the angle).
• Slope and gradient: from two levels and the distance, a rise and a run, or a slope typed as 1:100, 1 in 12, 2%, 5 deg or 0.01 with a length. You get the percent, the 1 in n, the angle, per thousand and the length along the slope, with a note on what the slope suits (1 in 12 is the usual most for a wheelchair ramp).
• Excavation and earthwork: the length and width at the bottom, the depth, the side slope (OSHA's slopes for digs under 20 ft deep: vertical for stable rock or shored sides, 1/2 to 1 short term or 3/4 to 1 for Type A soil, 1 to 1 for Type B, 1 1/2 to 1 for Type C), the soil's swell (typical, or your own figure) and what a truck holds. You get the volume in the ground (prismoidal formula), the loose volume, the truck loads, the size at the top and the weight at a typical 1,800 kg a cubic metre. In the US, OSHA asks for sloping, shoring or a trench box in any dig 5 ft (1.5 m) deep or more.

10. Pipe Flow

Choose what to find: the Pressure drop for a flow, the Flow a pipe carries for the head you can lose, or the Pipe size for a speed limit and a friction loss per 100 of length. Type the flow, the inside diameter (not the nominal size) and the length, choose the pipe material (typical roughness, or Own roughness) and the liquid (water and sea water follow the temperature; diesel, petrol, glycol and hydraulic oil are typical values at one temperature; or Own liquid with its density and viscosity), the rise from start to end, and the fittings and valves, with any other losses as a total K.

The answer gives the pressure drop and head, the speed (with a check against the usual 0.5 to 2 m/s for water), the friction in the pipe and in the fittings, the Reynolds number and the friction factor (64/Re when laminar, Colebrook-White when turbulent, Churchill's formula between 2,300 and 4,000), a bar of where the head goes and, for water, the Hazen-Williams result for comparison. For full pipes of liquid; for air, a rough guide at low pressure drops.

11. Pumps and Tanks

Pump power: type the flow and the total head (lift plus pipe losses; Pipe flow works out the losses), or the pressure the pump adds; the pump and motor efficiencies, the liquid, the motor margin, and the hours a day and price per kWh if you want the energy and its cost. The answer is the motor to choose, the next standard size above the pump's need (IEC 60072-1 and IS 12615 sizes in kW, the usual horsepower steps in US units), with the power into the water, the shaft power and the power from the supply.

Tank volume: choose a standing or lying cylinder, a lying tank with round ends, a box, a sphere or a cylinder on a cone, type its sizes and the liquid level (empty for full; for the cone, measured from its tip). You get what is in it and what it holds, the room left, the weight of water when full, a drawing and a level chart from empty to full. Under Is it big enough?, the people and the litres a person a day (IS 1172: 150 to 200 in cities over 1 lakh people with flush toilets, 100 to 150 in towns of 20,000 to 1 lakh) give the days a full tank lasts.

12. Torque, Pulleys and Gears

Torque, power and speed: type two of torque, power and speed to get the third (power = torque x angular speed; in shop units, kW = N m x rpm / 9,549 and hp = lbf ft x rpm / 5,252). Pulleys and gears: choose a belt (the two pulley diameters and the centre distance) or gears and sprockets (their teeth), and the speed of the driving shaft, with the power and efficiency for the torque. You get the driven speed, the ratio, the torque out and, for a belt, its pitch length, the wrap on the small pulley (under 120 degrees the belt may slip) and the belt speed. Belts slip 1 to 3%, so the real driven speed is a little lower.

13. Cable Size and Voltage Drop

1. Choose the supply (single phase, three phase or DC) and type the voltage (between lines for three phase), the load as a current or a power with its power factor, the cable length one way and the voltage drop you allow (IEC 60364-5-52 Annex G suggests 3% for lighting and 5% for other loads; the NEC 3% for a branch circuit).
2. Under Cable, choose mm2 and IEC or AWG and the US NEC, copper or aluminium, the insulation (PVC 70 C or XLPE 90 C) or the NEC temperature column (60, 75 or 90 C), how it is installed, the air temperature, and the circuits (IEC) or current-carrying wires (NEC) run together.

The answer is the smallest size that carries the current after the corrections, keeps the drop within your limit and is rated at least as much as the breaker, with the breaker (the next standard size above the load; the NEC also allows the next breaker above the wire's rating up to 800 A), the power lost in the cable and the longest run at that size. The table compares the sizes around it (Show every size lists them all). Copper ratings are those of IEC 60364-5-52 at 30 C (methods A1 and B1 up to 120 mm2) and NEC Table 310.16 (2023); aluminium on the IEC sizes is estimated at 75% of copper, on the safe side. Resistance is taken at the cable's full working temperature and the reactance at 0.08 milliohm a metre. Check the cable maker's table and your local rules, and have a licensed electrician check the circuit.

14. Current, Ohm's Law, Wire Gauges, Power Factor and Batteries

• Current, kW and kVA: the current from real or apparent power (or a motor's shaft power with its efficiency), or the power a current carries, for single phase, three phase and DC, with the apparent and reactive power.
• Ohm's law: type any two of voltage, current, resistance and power, and leave the other two empty. Choose a resistor rated at least twice the power.
• Wire gauge: start from an AWG or SWG size, a diameter or an area to get the others, the nearest AWG and SWG, the metric cable at least as big, the resistance at 20 C and, for AWG sizes, the NEC rating at 60, 75 and 90 C, with the AWG table (diameter = 0.127 mm x 92 to the power (36 - n)/39).
• Power factor correction: the kVAR to raise the power factor, the capacitance per phase (star or delta), and how much the current and the cable losses drop. Do not correct past 0.99.
• Battery backup: the battery's Ah, voltage and number in series, lead-acid or lithium, the usable depth (typical: 50% for lead-acid, 80 to 90% for lithium), the inverter's efficiency and the load. You get the backup time, the energy stored, the battery current, the Ah needed for the hours you want and the charging time (taking about 20% more charge than was used for lead-acid and 5% for lithium, typical figures). Above about C/4, a lead-acid battery gives less than its rated Ah.

15. Circuit Calculators

• Resistor colour code: read 3, 4, 5 or 6 bands, find the bands for a value (rounded to the figures the bands hold), or read an SMD code (472, 4702, 4R7, EIA-96 such as 01C). You also get the lowest and highest value within the tolerance, the SMD codes and the nearest E24 and E96 values.
• Capacitor code: read 104, 473J, 2A104K or 4n7, or find the code for a value, with the value in pF, nF and uF. A three-figure code holds two figures, so other values are rounded and the page says so.
• LED resistor: the supply, the LED colour (typical forward voltages) or your own forward voltage, the current, and the LEDs in a string and in all. You get the standard resistor for each string (the next one up keeps the current at or under the target), its power rating, the strings and the total current, with a drawing.
• Voltage divider: the output of two resistors with or without a load, or the best standard pair for the output you want with R1 + R2 in a range.
• Series and parallel: the total of resistors, capacitors or inductors in series and in parallel, and two standard resistors that make a value you want.
• RC, RL and LC timing: the time constant and cut-off frequency (with the charging curve), or the LC resonant frequency, and the reactance at a frequency.
• 555 timer: the frequency and duty cycle of an astable (time high 0.693 (R1 + R2) C, time low 0.693 R2 C), the pulse of a one-shot (1.1 R C), or the parts for a frequency and duty you want.
• PCB trace width: the width for a current by IPC-2221 (or the current a width carries), at the temperature rise, copper weight and layer you choose, with the trace's resistance, voltage drop and power.

16. Saving, Sharing and Printing

What you type is kept in this browser on this device, so it is there next time; nothing is written until you type or choose something. Share makes a link that opens the calculator with your numbers (they stay in the part of the link after #, which is never sent to a server, and the page takes them out of the address as it opens). Copy puts the numbers and the answer on the clipboard. Print prints a clean sheet with what you know, the answer, the drawing, the table and how it is worked out; the browser's own Print still prints the page as it is. Reset puts one calculator back to its example values, and Delete everything, in the Help window, removes EngCalc's data from this browser and leaves the rest of the site alone. The site's sun and moon button sets the light or dark theme.

17. Keyboard Shortcuts

Outside a text box: 1 to 6 open All and the five kinds, / finds a calculator, U switches SI and US units, and ? opens the help. On the tabs and the switches, the arrow keys move between them, with Home and End; on the beam's diagrams, they move along the beam (Shift for bigger steps). Esc closes a window. A link to the tool ending in a calculator's name (#beam, #column, #stairs, #pipe, #cable, #resistor and so on) opens that calculator.

18. How It Was Checked

Before it was published, the figures the tool states were checked against their sources: the ISMB table of IS 808:1989, the deflection limits of IS 800:2007 Table 6 and its column clause 7.1.2, the stair rules of the National Building Code of India 2016 (Part 3 clause 12.18 and Part 4), the US IRC and IBC limits, the water supply figures of IS 1172, the motor sizes of IS 12615:2018, the NEC's 2023 breaker sizes and Table 310.16, and the copper ratings of IEC 60364-5-52. Figures with no reliable source, or that differ in real life, are marked typical and can be replaced. The sums were then compared with a separate reference written from the rules on this page, with more than 22,000 cases: values typed in every unit and written many ways, beams against textbook formulas and a separate solution of more than 400 random beams, sections against hand formulas and polygon integrals, columns by every code, stairs, roofs, slopes and digs, pipe friction against the Colebrook equation and water against the standard tables, pumps, tanks against integration over the depth, belts, cables and their breakers, colour, SMD and capacitor codes both ways, LED, divider and timer parts against a search of every standard value, bar cutting, and damaged and hostile values. The page was then checked in the browser on phones and computers, in both themes, with an accessibility scan of every calculator and window.

19. Troubleshooting

• The beam says the supports cannot hold it still. One pin or roller lets it tip; add a second support or make one fixed.
• A box says it cannot read the value. Check the format (12.5, 25 mm, 12'6", 4k7) and the unit after the number; the line under the box says what went wrong.
• The cable says no single size is enough. Run cables in parallel, shorten the run, raise the voltage or choose another way of installing it.
• The staircase says the riser and tread must be at least 50 mm. Type them in millimetres or choose the unit beside the box.
• Values look wrong after changing units. Each box keeps the unit beside it; check the unit lists, or Reset the calculator.
• My numbers are gone. They are kept per browser and device; a private window or cleared browser data starts with the example values.

20. Support

For questions the FAQ does not answer, use the contact form. These calculators help with planning, checking and learning; for anything that carries people or power, have the design checked by a qualified engineer and follow your local code.