Field calculators
Field calculators by trade
Quick jobsite math, free and in your browser. Run the number here, then take the offline app and the record to the field. Just need units? Use the field unit converters.
Field calculator
Bolt torque calculator
Estimate bolt torque from the target preload: T = K x D x F, where K is the nut factor.
Field calculator
Sling load calculator
Find the tension in each sling leg: (load weight / legs) divided by the sine of the sling angle from horizontal.
Field calculator
Energy cost calculator
Find what a load costs to run: kWh = kW x hours, times the rate per kWh, per day and per year.
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Footcandle calculator
Estimate fixtures for a target light level: target lumens = area x footcandles, divided by the lumens each fixture delivers.
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Generator runtime calculator
Find how long a generator runs: usable fuel in gallons divided by the consumption in gallons per hour.
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Generator sizing calculator
Size a generator from the running load plus the largest motor's starting surge, with headroom: peak = running + surge.
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kVA to amps calculator
Convert kVA to full-load amps (or amps back to kVA) for single-phase and three-phase, from the voltage.
Field calculator
Markup & margin calculator
Convert between markup and margin and price a job right: enter your cost and a target margin, target markup, or price, and get the price, profit, markup %, and margin %.
Field calculator
Ohm's law calculator
Enter any two of voltage, current, resistance, and power, and the calculator solves the rest with Ohm's law.
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Watts to amps calculator
Find single-phase current from power: amps = watts divided by (volts x power factor).
Field calculator
Solar production calculator
Estimate solar energy: kWh = system kW x peak sun hours x a derate factor, per day and per year.
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Three-phase power calculator
Find three-phase kW and kVA from volts, amps, and power factor: kVA = sqrt(3) x V x A / 1000, and kW = kVA x PF.
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Voltage drop calculator
Size the conductor against the run: enter the load and length, get the volts dropped and the percent against the 3 percent target.
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CMU block calculator
Find blocks and mortar for a wall: about 1.125 standard 8x8x16 blocks per square foot, plus a bag of mortar per 28 to 32 blocks.
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Concrete bags calculator
Find how many bags of concrete a job needs: bags = volume (cubic feet) divided by the yield per bag, plus waste.
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Formwork pressure calculator
Estimate the lateral pressure of fresh concrete on column forms: P = Cw x Cc x (150 + 9000R/T).
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Concrete yardage calculator
Figure the cubic yards for a slab or footing from length, width, and thickness, with a waste allowance so you do not come up short.
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Dumpster calculator
Find how many roll-off containers a job needs: loose debris volume divided by the container size, in cubic yards.
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Drywall sheet calculator
Find how many drywall sheets a job needs: area to cover divided by the sheet size, plus waste.
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Truck load calculator
Find how many truck loads to haul off an excavation: loose volume = bank volume x (1 + swell), divided by truck capacity.
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Bearing pressure calculator
Check soil bearing pressure under a footing: pressure = load divided by footing area.
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Rebar weight calculator
Estimate the weight of reinforcing steel in pounds and tons from the bar size, the length per bar, and the number of bars, using the standard ASTM A615 unit weights.
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Sonotube concrete calculator
Find the concrete for round piers or columns: volume = pi x radius squared x height.
Field calculator
Stair calculator
Lay out a stair from the total rise: number of equal risers, the exact riser height, the tread count, and the total run.
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Stud count calculator
Find how many studs a wall needs: length divided by the on-center spacing, plus the corners and openings.
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ACH to CFM calculator
Find the airflow for a target air change rate: CFM = room volume x ACH / 60, from floor area and ceiling height.
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Ventilation rate calculator
Find the breathing-zone outdoor air a space needs: Vbz = Rp x Pz + Ra x Az.
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Tons to BTU calculator
Convert a cooling load to tons of refrigeration: tons = BTU per hour divided by 12,000.
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Dew point calculator
Find the dew point from air temperature and relative humidity, and the surface temperature condensation forms at.
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Duct equivalent diameter
Convert a rectangular duct to its equal-friction round diameter: De = 1.30 x (a x b)^0.625 / (a + b)^0.250.
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Affinity laws calculator
Scale fan or pump flow, pressure, and power for a speed change using the affinity laws: flow with speed, pressure with the square, power with the cube.
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Duct airflow calculator
Solve duct airflow and velocity from the duct size using continuity (Q = V x A): enter a round or rectangular duct and either the CFM or the velocity, and get the other.
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Hydronic load calculator
Find the heat load of a hydronic loop from flow and temperature difference: BTU/hr = GPM x 500 x delta-T, and tons = GPM x delta-T / 24.
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Mixed air temp calculator
Find the mixed air temperature from the outdoor and return temps and the outdoor-air percentage.
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NPSH available calculator
Find the net positive suction head available to a pump: NPSHa = atmospheric + static - vapor pressure - friction head.
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Pump BHP calculator
Find pump brake horsepower from flow and head: BHP = (gpm x head x specific gravity) / (3960 x efficiency).
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Sensible heat calculator
Find the sensible heat an airstream carries: BTU/hr = 1.08 x CFM x the temperature difference.
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Dehumidifier sizing
Size dehumidification for a water loss: AHAM pints per day = affected volume divided by the class factor.
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Pipe velocity calculator
Find water velocity in a pipe from the flow rate: V = 0.4085 x GPM / diameter squared, in feet per second.
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Pipe volume calculator
Find the water a pipe holds from its inside diameter and length: V = pi/4 x diameter squared x length, in gallons.
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Propane runtime calculator
Find how long a propane tank lasts: hours = usable tank energy divided by the appliance BTU load.
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Fill/drain time calculator
Find how long a tank takes to fill or empty: time = volume divided by flow rate.
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Tank volume calculator
Find the gallons in a vertical cylindrical tank from its diameter and height: V = pi/4 x diameter squared x height, in gallons.
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Pipe expansion calculator
Find how much a pipe run grows or shrinks: movement = length x coefficient x temperature change.
Field calculator
Water heating calculator
Find the heat to warm flowing water: BTU/hr = GPM x 500 x the temperature rise, with the kW equivalent.
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UPS runtime calculator
Estimate how long a battery or UPS holds a load: runtime = usable kWh x efficiency / load kW.
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PUE calculator
Find a data center's Power Usage Effectiveness: total facility power divided by the IT load, plus DCiE and the overhead in kW.
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Rack airflow CFM calculator
Find the CFM a rack needs from its kW load and the supply-to-return temperature rise: CFM = kW x 3412 / (1.08 x deltaT).
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Rack current & sizing calculator
Convert rack kW to amps (single or three phase) and size the continuous feeder and breaker at 80% per the NEC.
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Raised floor load calculator
Check the uniform load a cabinet puts on a raised access floor (psf) against the floor rating before you roll it into place.
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Redundancy capacity calculator
Find the usable capacity of a UPS, generator, or cooling plant under N, N+1, or 2N, and check it carries the critical load with a unit down.
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Fall clearance calculator
Find the clearance a personal fall arrest system needs below the anchor: free fall + deceleration + worker height + a safety margin.
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R-value thickness calculator
Find the insulation thickness for a target R-value: thickness = target R divided by the material's R per inch.
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Ladder setback calculator
Set a ladder safely with the 4 to 1 rule: base setback = height to contact divided by four.
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Coating coverage calculator
Find the paint or coating needed: gallons = area x coats / the coverage rate, plus waste.
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Roof squares calculator
Estimate roofing squares from the building footprint and the pitch: roof area = footprint x the pitch multiplier, and one square is 100 square feet.
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Aggregate base calculator
Find the tons of crushed aggregate base for a given area and compacted depth.
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Asphalt density calculator
Turn a mat density reading and the Gmm into % Gmm and air voids, and check it against the acceptance target before the lot cools.
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Asphalt tonnage calculator
Estimate the tons of hot-mix asphalt for a job from length, width, compacted thickness, and the mix unit weight, with a waste allowance.
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Soil swell/shrink calculator
Convert earthwork volume between bank, loose (haul), and compacted using swell and shrink: loose = bank x (1+swell), compacted = bank x (1-shrink).
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Trench volume calculator
Find excavation volume: length x width x depth in feet, divided by 27 for cubic yards, plus an approximate truck-load count.
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Bulk material calculator
Estimate the cubic yards, cubic feet, bags, and tons of mulch, gravel, topsoil, or sand for a bed or area from length, width, and depth.
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Deck board calculator
Find the deck boards for a deck: boards = deck area divided by the coverage of one board, plus waste.
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Drip run time calculator
Find a drip zone's precipitation rate and run time: rate = GPH x 1.604 / area, and run time = target depth divided by the rate.
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Fence post calculator
Find the posts, sections, and rails for a fence run: sections = length divided by post spacing.
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Precipitation rate calculator
Find how fast a zone applies water: PR (in/hr) = 96.25 x total gpm / zone area, and the run time to hit a target depth.
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Paver count calculator
Find how many pavers or bricks an area needs: area divided by the coverage of one unit, plus a waste allowance for cuts and breakage.
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Runoff calculator (Q=CiA)
Estimate peak stormwater runoff from a small site with the rational method: Q = C x i x A, in cubic feet per second.
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Retaining wall calculator
Find the segmental wall blocks for a wall: face blocks = wall face area divided by the block face area.
Field calculator
Slope and grade calculator
Turn rise and run into percent grade, degrees, a run-to-rise ratio, and inches per foot for grading, drainage, and ramps.
Field calculator
Sod & seed calculator
Find the sod (square feet and pallets) or grass seed (pounds) to cover an area.