Science & Engineering Calculators

Enter any two of voltage, current, resistance or power and get the other two, with every formula in the Ohm’s law wheel shown.

Calculate voltage drop over a cable run from length, size and current, and check it against the usual 3% and 5% limits.

Work out what any appliance costs to run per hour, day, month and year from its wattage and your tariff.

Calculate density, mass or volume from the other two, with a reference table of common materials and a float-or-sink check.

Calculate the wind chill temperature — how cold the air feels on exposed skin — using the official North American formula.

Calculate the heat index — how hot it feels once humidity is accounted for — with the official NWS regression and risk categories.

Calculate dew point from temperature and humidity using the Magnus formula, with what each dew point actually feels like.

Solve for molarity, mass, volume or moles when preparing a solution — enter any three of the four to find the fourth.

Calculate the molecular (molar) weight of a chemical formula — supports parentheses and hydrates like CuSO₄·5H₂O.

Solve PV = nRT for pressure, volume, moles or temperature, with unit conversion and a check on how ideal the conditions really are.

Convert between pH, pOH and hydrogen ion concentration, and find the pH of a strong or weak acid or base from its concentration.

Read a resistor's value and tolerance from its colour bands — supports 3-band, 4-band and 5-band resistors.

Combine capacitors in series or parallel, with total capacitance, stored energy, charge and the voltage each series capacitor carries.

Calculate the RC time constant, charging and discharging voltage over time, and the filter cutoff frequency of a resistor–capacitor circuit.

Convert AWG to diameter, cross-section and resistance per metre, with metric equivalents and reference ampacity figures.

Calculate horsepower from torque and RPM, or convert between horsepower, kilowatts and metric horsepower.

Estimate horsepower from a quarter-mile ET or trap speed, or predict the ET and trap speed a given horsepower should run — the classic drag racing formulas, both directions.

Estimate the air conditioner size (in BTU) a room needs, from its dimensions, insulation, sun exposure and occupancy.

Calculate the escape velocity and surface gravity of a planet, moon or star from its mass and radius.

Calculate kinetic energy, mass or velocity from KE = ½mv², with momentum and stopping distance alongside.

Calculate the range, maximum height and flight time of a projectile from its launch speed and angle.

Calculate terminal velocity from mass, drag coefficient and frontal area, with the distance and time needed to reach it.

Work out gear ratio from tooth counts, with output speed, torque multiplication, and multi-stage or compound gear trains.

Calculate the heat energy needed to change a substance's temperature from Q = mcΔT, solving for any variable.

Convert between wavelength, frequency and photon energy for light, sound and any other wave.

Calculate the electrostatic force between two charges, or solve for charge or separation, with the force compared against gravity.

Combine resistors in series or parallel, with the current and power dissipated in each one when a voltage is applied.

Combine multiple sound sources, convert between decibels and ratios, and work out how loudness falls with distance.

Size a home electrical service by the NEC 220.82 optional method, or test whether an existing panel can take an EV charger using the 220.87 measured-demand route.

Compare the total cost of owning an electric car against a petrol one across purchase, depreciation, fuel, maintenance and insurance, and find the year the EV pulls ahead.

Size a standby or portable generator from your actual loads, using running watts plus the single largest starting surge rather than the sum of every surge on the list.

Compare what a heat pump and a gas, propane, oil or electric system cost to run for the same amount of delivered heat, and find the electricity price where they break even.

Work out how many hours a home battery will actually run your essential loads once depth of discharge and round-trip losses are taken off, and how much solar it takes to last indefinitely.

Work out the annual heating and cooling saving from adding attic insulation, using degree days and your own fuel prices, and how many years the job takes to pay back.

Work out how many solar panels and how many kilowatts your house needs to offset its electricity use, from your consumption, your sun hours and your roof orientation.

Compare a time-of-use electricity tariff against a flat rate using your own peak, off-peak and shoulder split, and find the peak share where the plan stops paying.

Work out what your hot water costs to produce each year on electric, heat pump, gas tank, tankless or propane, and how long a more efficient unit takes to pay for itself.

Calculate the real annual heating and cooling saving from replacing windows, using U-factors and degree days, and compare it honestly against the cost of the job.

Work out the CADR an air purifier needs for your room at a chosen number of air changes per hour, check what a unit you are considering actually achieves, and see the running cost.

Work out what size dehumidifier a room or basement needs on the current post-2019 pint scale, with the running cost, and the old-scale equivalent so older charts can be compared.

Size a round or rectangular duct for a given airflow using the equal-friction method, check the air velocity against noise limits, and see what flexible duct costs you.

Work out the whole-house mechanical ventilation your home needs under ASHRAE 62.2, the fan size for intermittent running, and the kitchen and bathroom exhaust that goes with it.

Size a water softener from your hardness, iron content and household size, and see how often it will regenerate, how much salt it will use and what that costs each year.

Work out how many minutes each sprinkler zone should run from its precipitation rate and your weekly water requirement, and whether the soil needs cycle-and-soak.

Estimate what it costs to heat a swimming pool across a season on gas, propane or a heat pump, and see how much of that a cover saves by suppressing evaporation.

Work out how many gallons a swimming pool holds for any common shape and depth profile, plus the pump flow needed to turn the whole volume over through the filter.

Size a sump pump from the water inflow you actually measure in the pit rather than from basement square footage, and check it against the head your discharge line imposes.

Size a submersible well pump by working out peak flow demand and total dynamic head, including the pressure and friction terms that most rules of thumb leave out.

Work out how long a battery bank takes to charge from solar, shore power and an alternator combined, including the slow absorption phase that lead-acid cannot skip.

Work out how long a battery will actually run a load, with Peukert losses, depth of discharge and temperature applied — not just capacity divided by current.

Size low-voltage DC wire for 12, 24 or 48 volt systems against both voltage drop and ampacity, and see which of the two is actually limiting your run.

Size an off-grid or RV inverter from your loads, and see the DC input current, battery cable and fuse it needs — the numbers that decide what the install actually costs.

Size an off-grid or RV battery bank in amp-hours from your daily loads, days of autonomy, depth of discharge, round-trip losses and the temperature it will actually live at.

Work out how long a propane tank lasts for your appliances, what it costs to run them, and whether cold weather will limit the tank before the propane runs out.

Work out what a 30 or 50 amp RV shore power connection can actually run at once, why 50 amp gives more than three times the capacity, and how to balance the two legs.

Size a van or RV solar array from your daily amp-hours, with the flat-mounting and winter penalties applied, a roof-space check, and how much driving would replace it.

Size an MPPT or PWM solar charge controller from your array and battery voltage, and check the cold-morning open-circuit voltage that destroys undersized controllers.

Find the optimal solar panel tilt for your latitude — year-round, seasonal or winter-biased — and see how little output you actually lose by being a few degrees off.

Find the ball mount drop or rise that tows your trailer level, allowing for rear suspension squat, and see what being out of level actually costs.

Check your trailer tongue weight against the safe range, see whether it is light enough to sway or heavy enough to overload the hitch, and find how far to move cargo to fix it.

Work out the heaviest trailer your vehicle can legally and safely pull, checked against all four limits at once — tow rating, GCWR, payload and the hitch.

Work out the power needed to hold a speed while towing, split into rolling, aerodynamic and grade, with altitude and temperature applied to the engine.

Estimate fuel economy and trip cost while towing, from road-load physics rather than a rule of thumb — and see why a trailer’s shape costs more than its weight.

Work out how far a loaded combination takes to stop with and without trailer brakes, on grades and wet roads, and check the weight thresholds that require them.

See how each item you load changes tongue weight, which ones are pulling it dangerously low, and exactly how far to move something to bring the balance back.

Work out the load on each trailer tyre, check it against the sidewall rating, and apply the 65 mph speed rule that decides whether that rating actually applies.

Add up everything your vehicle is carrying — people, cargo, accessories and trailer tongue weight — and see how much payload is left, or how far over you are.

Size weight-distribution spring bars and set them up by measurement, using front axle load restoration and fender heights rather than guessing at level.

Size a coop, run, roost and nest boxes for your flock, work out feed and water, and see what the eggs actually cost against the shop.

Work out the real carbon-to-nitrogen ratio of a compost pile by mass, find how much more of one material it needs, and check the pile is big enough to heat.

Convert a nitrogen rate into pounds of actual product for your N-P-K analysis, check it against the annual limits, and price it per pound of nitrogen.

Convert a woodpile into cords, work out the heat it will actually deliver at your moisture and appliance, and price it against propane, gas and electricity.

Work out how much grass seed a lawn needs by species, with separate rates for a new lawn and for overseeding, plus seeding windows and cost.

Size a greenhouse heater from glazing area rather than floor area, and price a season of heat across fuels, set points and glazing choices.

Work out how many plants fit a bed at a given spacing, compare square and offset layouts, and see the 15% more that staggering the rows buys you.

Work out how much water a roof collects per inch of rain and per year, size a tank against real garden demand, and see how much of it would overflow.

Work out how much lime or sulphur it takes to move your soil pH, allowing for soil texture, the material’s neutralising value and the cap on a single pass.

Work out the heat load of the space a wood stove has to warm, find the output and firebox size that suit it, and see why oversizing is the expensive mistake.

Work out spa-sized doses of chlorine or bromine, how fast dichlor drives cyanuric acid up, and when the water is due for replacement.

Work out the baking soda to raise total alkalinity, or plan the acid-and-aeration cycles that lower it without driving pH into the aggressive range.

Work out the calcium chloride to raise hardness, how much water to replace to lower it, and what a season of cal-hypo and evaporation adds on their own.

Work out how much of any chlorine product raises your pool to a target level, and what a whole season of that product does to cyanuric acid and hardness.

Work out the Langelier Saturation Index from pH, alkalinity, calcium and temperature, and see which single change brings aggressive or scaling water back into balance.

Work out the muriatic acid or soda ash a pool needs to reach a target pH, and what the correction does to total alkalinity at the same time.

Work out the salt a chlorine generator needs, how much water to replace if it is too salty, and how much salt liquid chlorine adds on its own.

Work out the chlorine needed to reach breakpoint and destroy chloramine, or the level to hold for algae, and see why a dose that falls short makes it worse.

Work out how much cyanuric acid raises a pool to target, and how much water must be replaced to bring an over-stabilised pool back down.

Tell a leak from ordinary evaporation using the bucket test, convert the loss into gallons and money, and check it against what evaporation should be.

Size a compressor by the CFM your tools actually need, and work out how long the tank lasts before the motor has to catch up.

Work out how many clamps a glue-up needs and how far apart, from the joint area and the target pressure for the wood’s density.

Size shop dust collection by duct velocity rather than horsepower: required CFM, whether your duct keeps chips moving, and the static pressure the run costs you.

Work out how much water has to leave a stack of green lumber, what it will weigh and shrink to, and the moisture content air drying can actually reach.

Work out what a stack of lumber weighs at any moisture content, by species, and whether the vehicle you are collecting it in can legally carry it.

Work out feed rate, chipload and safe spindle speed for a router or CNC, and see why feeding too slowly is what burns bits rather than feeding too fast.

Compound miter and bevel angles for frames, bevelled boxes, crown moulding and segmented rings, from one pair of equations rather than four charts.

Work out how far a shelf will bend under load from its span, thickness and material, and what a front lip or a shorter span would do about it.

Work out how much finish a project needs, allowing for the first coat soaking into bare wood and for what spraying loses to overspray.

Work out how much a board will shrink and swell across the seasons using the Forest Products Laboratory coefficients, and what the joinery has to allow for.

Work out the net free ventilating area an attic needs under the 1/150 and 1/300 rules, how it must be split between intake and exhaust, and how many vents that is.

Size a chimney flue to NFPA 211 from the appliance collar or the fireplace opening, including the maximum area that is allowed and the 3-2-10 height rule.

Work out how much de-icer a driveway actually needs at the agency rate, whether your product works at the temperature, and what the chloride does downstream.

Work out how long a pipe has before it freezes, how much time insulation buys, and how small a drip actually has to be to stop it.

Size gutters and downspouts from roof area and local rainfall intensity, using code capacities rather than the one-size-fits-everywhere rule of thumb.

Work out whether your attic is warm enough to melt the snow on your roof, how fast, and which of air sealing, insulation or ventilation would actually stop it.

Work out how much de-icing cable a roof needs, how high the zigzag has to reach to actually work, and what it costs to run for a winter.

Convert roof pitch between rise per 12, degrees and percent grade, and get rafter lengths, the true roof area from a footprint, and the minimum pitch each covering needs.

Work out the design snow load on a roof by ASCE 7, including the minimum that governs at low ground snow, and weigh the snow that is up there now.

Work out whether your windows will run with condensation, and the maximum indoor humidity they can take at any outdoor temperature.

Work out bend allowance, bend deduction and the flat pattern length for sheet metal, with the K-factor taken from the radius-to-thickness ratio.

Work out fillet weld capacity by AISC 360, in LRFD or ASD, with the base metal check and the minimum and maximum leg sizes the code requires.

Work out what a piece of steel, aluminium, stainless or brass weighs from its shape and dimensions, per foot and per piece, with cost and a material comparison.

Work out carbon equivalent and the preheat a steel needs, from composition or grade, thickness and the hydrogen level of the consumable.

Convert sheet metal gauge to thickness for steel, galvanised, stainless and aluminium - four different standards - with weight per sheet.

Work out shielding gas flow, how long a cylinder lasts, and the cost per hour and per foot of weld - and why turning the flow up makes porosity worse.

Calculate arc energy and heat input to AWS D1.1, in kJ per inch and per millimetre, with the process efficiency that separates the two.

Work out a welding machine’s duty cycle at any current, how many minutes of arc that allows in ten, and the current it will run at continuously.

Find a starting amperage for stick, MIG or TIG from the electrode or wire size and the material thickness, with wire feed speed and voltage.

Work out deposition rate, the weld metal a joint needs, arc time and consumable cost - with the deposition efficiency that separates wire bought from weld deposited.

X and Y coordinates for any bolt circle, plus the chord between holes - and the reverse, working out an unknown bolt circle from a measurement.

Convert surface speed to spindle RPM for milling, turning and drilling, in inch or metric, with the recommended speed band for the material and tool.

Work out drill point length and the true depth to programme, so a blind hole reaches full diameter and a through hole actually breaks out.

Work out cutting time, cycle time and cost per machined part, with tool life priced in through Taylor's equation and the economic cutting speed found.

Work out metal removal rate, spindle horsepower, torque and cutting force for milling, turning or drilling, with specific cutting force that varies with chip thickness.

Work out milling feed rate from chip load, flutes and spindle speed, with the radial chip thinning correction that light stepovers make essential.

Gauge block stack for any sine bar angle, the angle from a stack, and taper conversions - with the accuracy the setup really has at that angle.

Work out theoretical surface finish from feed and nose radius, or the feed a target Ra needs, with conversion between Ra, Rz, RMS and ISO N grades.

Find the tap drill for any inch or metric thread at a chosen percent of engagement, with the thread the hole really gets once drill oversize is allowed for.

Pitch, minor and major diameters for any 60 degree inch or metric thread, with three wire measurement, best wire size and tensile stress area.