EngCalc FAQ
Questions and answers about the engineering calculators. Everything they work out happens in your browser.
Last Updated: November 9, 2026
1. General Questions
Q1: What is EngCalc?
A1: Twenty-eight calculators for engineers, builders, electricians and makers, in five kinds: Structure (beams, sections, columns), Building (steel bars, metal weight, stairs, roof pitch, slope, digging), Fluids and machines (pipe flow, pumps, tanks, torque, pulleys and gears), Electrical (cable size, current from kW, Ohm's law, wire gauges, power factor, battery backup) and Circuits (resistor and capacitor codes, LED resistors, dividers, series and parallel parts, RC and LC timing, the 555 timer, PCB traces). Answers change as you type, and each one shows how it is worked out.
Q2: How much does it cost?
A2: Nothing. It is free, with no registration and no limit. Like every page on ZeroDataUpload, it is supported by advertising.
Q3: Do I need to install anything or create an account?
A3: No. Open the page in any modern browser (Chrome, Edge, Firefox, Safari or Opera) on a computer, tablet or phone. What you type is kept in that browser, so there is nothing to sign in to.
Q4: Is anything I type uploaded?
A4: No. Every number is worked out by this browser on your device and never sent to a server. The page itself loads the site's ads and analytics, as every page on the site does; the Privacy Policy explains those, and your numbers are never part of them.
Q5: Who is it for?
A5: Engineering students checking homework, site engineers and contractors working out steel, stairs and digging, plumbers and mechanical engineers sizing pipes and pumps, electricians choosing a cable and its breaker, and makers reading resistor codes or designing an LED string or a 555 timer.
Q6: Can I use it for a real design?
A6: Use it for planning, checking and learning. It follows the codes it names, but it does not know everything about your job: load combinations, lateral bracing, local buckling of thin plates, fire, fatigue, earthing and your local rules. Anything that carries people or power needs a design by a qualified engineer or a licensed electrician under your local code.
2. Typing Numbers and Units
Q7: What can I type in a box?
A7: A number (12.5), a number with a unit after it (25 mm, 3.5 kN, 12 kN/m), feet and inches (12'6", 6' 4 1/2"), fractions (3/8, 1 1/2 in), sums (2*450 + 30), and the shorthand printed on parts (4k7 is 4.7 kilohms, 2R2 is 2.2 ohms, 100n is 100 nanofarads). Thousands may have commas (1,200 or 1,00,000), and a single comma between digits is read as a decimal point (2,5). The line under the box shows what was understood, or says it cannot read it.
Q8: What do the small lists beside the boxes do?
A8: They set the unit of that one box. Changing the unit keeps the size: 6 m becomes 6000 mm. A unit typed after the number wins over the list, so 25 mm in a box set to metres is still 25 mm.
Q9: What does the SI and US switch do?
A9: It sets every calculator to metres, newtons and pascals or to feet, pounds and psi, and converts what you typed in the other system's units, to five significant figures. Press U to switch from anywhere in the tool. Volts, amps, seconds and degrees belong to both systems and are left alone.
Q10: Why does a box say a number is too large or too long?
A10: A box takes at most 60 characters, and values beyond what an engineering calculation needs (a million billion in the box's base unit) are refused, as is a temperature below absolute zero. Saved values and shared links pass the same checks.
3. Beams
Q11: What beams can the beam calculator solve?
A11: Any straight beam: simply supported, a cantilever, fixed at both ends, fixed and propped, with an overhang, continuous over 2 to 6 equal spans, or your own pinned, roller and fixed supports anywhere (up to 12). Loads can be point loads, spread loads, loads that vary from one end of a stretch to the other, and moments, up to 30 in all, plus the weight of the beam itself.
Q12: Which way are loads and moments positive?
A12: Loads are downward when positive, so type a negative number for a load that lifts. Moments are clockwise when positive. In the reactions table, upward forces and anticlockwise moments on the beam are positive.
Q13: How accurate is it?
A13: The reactions, shear and moment follow from balancing the forces, and the deflection from hundreds of short beam elements with a node at every support and load, so the results are those of an elastic beam to within rounding, a few parts in 100,000. Before it was published it was compared with textbook formulas and with a separate solution of more than 400 random beams. Shear deformation is left out, as is usual for beams longer than about five times their depth.
Q14: What do the stress and sag checks compare with?
A14: Bending stress (moment over the section modulus) against 0.66 times the yield strength, the usual working limit for steel in bending when the compression flange is held sideways; timber against its characteristic bending strength. Average shear in the web against 0.4 times the yield strength. Sag against the limit you choose, from span/180 to span/360, with free ends checked against twice their length (the codes allow a cantilever twice the sag over its length).
Q15: Which sag limit should I choose?
A15: IS 800:2007 Table 6 gives span/300 for floors and roofs where the finishes do not crack and span/360 where they do; IS 456 gives span/250 for the final sag of a concrete member and span/350 after partitions and finishes are built; the US IBC gives span/360 for floors under live load, span/240 under total load and span/180 for roof members without a ceiling.
Q16: Do I need to add load factors?
A16: For strength, yes: the loads are used as you type them, so multiply them by your code's factors (1.5 in IS 456 and IS 800, 1.2 dead plus 1.6 live in ASCE 7). For sag, use the loads without factors.
Q17: Can I read the values anywhere along the beam?
A17: Yes. Point at the diagrams, or press Tab to reach them and use the arrow keys (Shift for bigger steps, Home and End for the ends). The line under them gives the position, shear, moment and deflection there. Save the values (CSV) writes them every two hundredth of the length for a spreadsheet.
4. Sections and Columns
Q18: Which sections can I use?
A18: A rectangle, a hollow rectangle (box), a round bar, a round tube, an I-beam, a channel, a T-section and an angle, typed by their sizes, or the Indian standard medium weight beams ISMB 100 to ISMB 600. In the beam and column calculators you can also type your own moment of inertia, section modulus and area.
Q19: Where do the ISMB values come from?
A19: From IS 808:1989, Table 2.1, read from the standard: the mass, sizes, area, moments of inertia and section moduli, which include the sloping flanges and root fillets. IS 808:2021 has since replaced the 1989 edition, so check the mill's table for a design.
Q20: What is the plastic modulus, and the torsion constant?
A20: The plastic modulus is the first moment of the two halves of the area about the axis that splits it in two; it gives the moment at which the whole section yields. The torsion constant is exact for round bars and tubes and from Bredt's formula for boxes; for open shapes it is the usual thin-walled estimate. Corners and fillets are taken as sharp, except in the ISMB table values.
Q21: How is the column strength worked out?
A21: The slenderness is the effective length over the radius of gyration. Euler's load is the limit for a perfect column. The design strength follows IS 800:2007 clause 7.1.2 (with its buckling classes a to d and a partial factor of 1.10), EN 1993-1-1 clause 6.3.1 (with curve a0 as well, and a factor of 1.0) or AISC 360-16 chapter E (LRFD with 0.9, or ASD with 1.67). The table shows every code side by side, with the Johnson parabola for comparison.
Q22: Which effective length factor should I use?
A22: The end conditions list gives the theoretical K (0.5 for both ends fixed up to 2 for a flagpole). With "Use the design value of K" ticked, the larger values the codes recommend are used (0.65, 0.8, 1.0, 1.2, 2.1 and 2.0), because real ends are never perfectly fixed. You can also type your own K.
Q23: Which buckling curve applies to my section?
A23: Rolled I-sections about the strong axis use curve a, about the weak axis b; welded boxes and cold-formed hollow sections b under IS 800 and c under Eurocode; channels, tees and solid bars c; angles c under IS 800 and b under Eurocode; thick welded I-sections about the weak axis d. Curve a0 is in Eurocode only, for hot-finished hollow sections in high-strength steel; with IS 800 the page uses curve a for it and says so.
5. Building
Q24: Where are concrete, cement and bricks?
A24: In HomeCalc, our home and property calculators, in its Cement and bricks tab: concrete by the nominal mixes of IS 456 (M5 to M20) with the water the standard allows, bricks and blocks with their mortar, and plaster. EngCalc's Building tab has a link that opens it, so the same sums are not kept in two places.
Q25: How is the steel for bars worked out?
A25: Each bar's weight a metre is d squared over 162.2 (d in mm), the weight of a round bar of steel at 7,850 kg a cubic metre. A bar longer than the stock length is made of pieces joined with a lap of 40, 50 or 60 times its diameter. The pieces of each diameter are cut from stock bars largest first, each into the bar it fits most tightly, so the offcuts are few; above 4,000 pieces of one diameter, the bars to buy are estimated from the total length.
Q26: Which building codes does the staircase follow?
A26: India's National Building Code 2016: risers at most 190 mm and treads at least 250 mm in one- or two-family homes, 150 and 300 mm in flats, hostels and other buildings, at most 12 risers a flight, 2.2 m of headroom, and widths of 1.0, 1.25 or 1.5 m. The US IRC for homes and IBC for other buildings, and the UK's Approved Document K for a private stair. Blondel's comfort rule (two risers plus a tread between 600 and 650 mm) is checked as well.
Q27: What side slopes does the digging calculator use?
A27: OSHA's slopes for excavations under 20 ft (6 m) deep: vertical for stable rock or shored sides, 3/4 to 1 for Type A soil such as stiff clay (1/2 to 1 for short-term work up to 12 ft deep), 1 to 1 for Type B soil, and 1 1/2 to 1 for Type C soil such as sand, gravel and wet or loose soil. The volume uses the prismoidal formula, which is exact for a pit with even sloping sides.
Q28: Why does dug soil need more trucks?
A28: Soil swells once it is dug: sand by about 10%, common earth by about 25%, clay by about 35% and blasted rock by about 50%. These are typical figures; choose Own figure if you know your soil's. The truck loads are the loose volume over what a truck holds.
6. Fluids and Machines
Q29: How is the pressure drop in a pipe worked out?
A29: By Darcy-Weisbach: the friction factor is 64 over the Reynolds number for laminar flow and from the Colebrook-White equation for turbulent flow, with Churchill's formula between them. Fittings and valves add K times the velocity head, and a rise adds its height. For water the Hazen-Williams result is shown for comparison.
Q30: Where do the roughness and fitting figures come from?
A30: They are typical values for new pipe and common fittings from Moody's chart and makers' tables; real figures differ with size, age and maker. Choose Own roughness to type the pipe maker's figure, and type extra losses as a total K for anything not listed.
Q31: Which liquids can I use?
A31: Water and sea water, whose density and viscosity follow the temperature you type, and air at low pressure. Diesel, petrol, 30% ethylene glycol and ISO VG 46 hydraulic oil are typical values at one temperature, shown in their names. Choose Own liquid to type a density and a viscosity in mPa s (the same number as centipoise).
Q32: How does the pump calculator choose a motor?
A32: The power into the water is density times g times flow times head; the pump's shaft power is that over the pump's efficiency, and the margin you choose is added on top. The motor is the next standard size above it: the IEC 60072-1 and IS 12615 sizes in kW, or the usual US horsepower steps. Small pumps run at about 30 to 50% efficiency and large ones at 70 to 85%; the pump curve gives the real figure.
Q33: How much water does a family need?
A33: IS 1172 suggests 150 to 200 litres a person a day in cities of over 1 lakh people with flush toilets and 100 to 150 litres in towns of 20,000 to 1 lakh. Type the people and the litres a day under "Is it big enough?" to see how many days a full tank lasts.
7. Electrical
Q34: How is the cable size chosen?
A34: The rating of each size is corrected for the air temperature and for circuits (IEC) or current-carrying wires (NEC) run together. The size chosen is the smallest that carries the load current, keeps the voltage drop within your limit over the length, and is rated at least as much as the breaker, which is the next standard size above the load (the NEC allows the next breaker above the wire's rating up to 800 A). The table compares the sizes around it.
Q35: Which rating tables are used?
A35: For copper, IEC 60364-5-52 at 30 C, for methods A1 (in conduit in an insulated wall), B1 (in conduit on a wall), C (clipped direct) and E (on a tray in free air), PVC or XLPE, with two loaded conductors on single phase and DC and three on three phase; A1 and B1 are listed up to 120 mm2. In US mode, NEC Table 310.16 (2023) at 60, 75 or 90 C, with 14, 12 and 10 AWG copper held to 15, 20 and 30 A by 240.4(D).
Q36: Why is aluminium an estimate?
A36: On the IEC sizes, aluminium is rated at 75% of copper. That is a little below the 78% the two metals' resistance gives, so it errs on the safe side, but it is not the aluminium table of IEC 60364-5-52, which is not free to read. Check that table or the cable maker's figures before you buy. The NEC aluminium column is the standard's own.
Q37: What voltage drop should I allow?
A37: IEC 60364-5-52 Annex G suggests 3% for lighting and 5% for other loads on a supply from the public network; the NEC suggests 3% for a branch circuit and 5% in all. The drop is worked out with the cable at its full working temperature, so it is on the safe side.
Q38: How do I find the current of a motor?
A38: Under Current, kW and kVA, type the motor's power and tick "It is a motor's output (shaft) power" with its efficiency, and its power factor. The nameplate current is the better figure if you have it; starting current is 6 to 8 times higher on a direct-on-line start.
Q39: How is a power factor capacitor sized?
A39: The kVAR is the real power times the change in the tangent of the angle, from the power factor now to the one you want. The capacitance per phase is the kVAR over 2 pi f V squared for single phase and star-connected banks, and a third of that for delta. Do not correct past 0.99: a leading power factor raises the voltage at light load.
8. Circuits
Q40: How do I read a resistor's colour bands?
A40: Hold it with the bands closest together on the left; the tolerance band is often set apart, and gold or silver is never first. Choose 3, 4, 5 or 6 bands and pick each colour. Three and four bands give two figures and a multiplier, five and six give three figures; the sixth band is the temperature coefficient. Find bands does the reverse, and SMD code reads 472, 4702, 4R7 and EIA-96 codes such as 01C.
Q41: How do I read a capacitor code?
A41: Two figures and the number of zeros, in picofarads: 104 is 10 and four zeros, 100,000 pF or 100 nF. A third figure of 8 or 9 means times 0.01 or 0.1. A letter after the code is the tolerance (J 5%, K 10%, M 20%), and a figure and letter before it is the voltage (1H is 50 V, 2A is 100 V, 2J is 630 V). Codes such as 4n7 put the unit where the point goes.
Q42: What resistor does an LED need?
A42: The supply voltage less the LEDs' forward voltages in the string, divided by the current. EngCalc picks the next standard value up in the range you choose, so the current stays at or under the target, and a power rating at least twice what the resistor takes. The forward voltages in the list are typical; the LED's data sheet gives the real one. Never put LEDs in parallel on one resistor.
Q43: How does the 555 timer design work?
A43: Type the frequency and the duty cycle. EngCalc takes the first standard capacitor from 1 nF to 100 uF that keeps both resistors between 1 kilohm and 1 megohm, then the nearest standard resistors, and shows the frequency and duty they really give. Below 50% duty, a diode across R2 is needed.
Q44: How wide should a PCB trace be?
A44: By IPC-2221: the current is k times the temperature rise to the power 0.44 times the cross-section (in square mils) to the power 0.725, with k 0.048 for outer layers and 0.024 for inner ones. EngCalc solves it for the width at your copper weight, with the trace's resistance, voltage drop and power. IPC-2221 errs on the safe side, most of all for inner layers.
9. Saving and Sharing
Q45: Where are my numbers kept?
A45: In this browser on this device, under one name with the tool's prefix, so they are there next time. Nothing is written until you type or choose something. A private window, another browser or cleared browser data starts with the example values.
Q46: How do I share a result?
A46: Share makes a link that opens the calculator with your numbers. They ride in the part of the link after #, which the browser never sends to a server, and the page takes them out of the address as it opens. On a phone, Share opens the phone's share sheet; elsewhere the link is copied.
Q47: How do I start again or remove everything?
A47: Reset puts one calculator back to its example values. Delete everything, in the Help window, puts every calculator back, clears your favourites and recent calculators, and removes EngCalc's data from this browser; the rest of the site is left alone.
Q48: Does it work offline?
A48: Once the page has loaded, the calculators work without the internet, since everything is worked out in the browser. The page is not installed as an app; reopening it needs a connection.
Still have a question?
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