HVAC & Mechanical Calculators
Airflow, loads, duct sizing, and refrigeration.
Electrical
10 TOOLSNEC code checks and electrical design calculators.
- VDVoltage Drop CalculatorNEC Table 9 voltage drop with the 3% branch check.
- AMPWire Ampacity & Derating CalculatorDerated ampacity per NEC Table 310.15(B)(16).
- FILLConduit Fill CalculatorMixed-conductor fill vs. 53 / 31 / 40% limits.
- BOXBox Fill CalculatorNEC 314.16 volume vs. conductor & clamp counts.
- FLAMotor FLA CalculatorFLA from HP, voltage & phase per NEC tables.
- kVATransformer Sizing CalculatorkVA and amps, single- and three-phase.
- LOADService & Load CalculatorDwelling & commercial loads to size the service.
- BENDConduit Bending CalculatorOffset & saddle multipliers, shrink & marks.
- ΩOhm's Law & Power CalculatorVolts, amps, ohms & watts from any two values.
- GENGenerator Sizing CalculatorRunning & starting kW with motor inrush.
Plumbing
7 TOOLSPipe sizing, flow, drainage, and capacity.
- VOLPipe Volume & Capacity CalculatorGallons per foot & total fill by pipe size.
- ¼"Drainage Pipe Slope CalculatorFall over a run and the minimum-grade check.
- PSIWater Pressure Loss CalculatorFriction loss through pipe & fittings at GPM.
- DFUFixture Unit CalculatorDFU / WSFU totals from fixture counts.
- SIZEPipe Sizing CalculatorDiameter from flow, length & allowable loss.
- TANKTank Volume CalculatorCylinder, rectangle & oval capacity in gallons.
- GPMGPM Flow Rate CalculatorGPM from pipe size & velocity — or the reverse.
HVAC & Mechanical
6 TOOLSAirflow, loads, duct sizing, and refrigeration.
- DUCTDuct Size CalculatorRound & rect sizes from CFM and friction rate.
- CFMCFM & Airflow CalculatorCFM from room volume and target air changes.
- BTUBTU & Heat Load CalculatorBTU/hr load from area, climate & construction.
- TONCooling Tonnage CalculatorBTU/hr to tons of cooling, and back.
- ESPStatic Pressure CalculatorTotal ESP from duct, coil & filter losses.
- REFRefrigerant Line Charge CalculatorAdded charge for line length past pre-charge.
Carpentry & Framing
6 TOOLSLumber, framing, stairs, rafters, and decking.
- BDFTBoard Foot CalculatorBoard feet & cost from nominal size and count.
- STUDStud & Framing CalculatorStuds, plates & lineal feet from wall length.
- STRStair CalculatorRiser, tread & stringer layout from total rise.
- RFTRRafter & Roof Pitch CalculatorRafter length & cuts from pitch and span.
- JOISTJoist Span CalculatorAllowable spans by species, size & spacing.
- DECKDecking CalculatorBoards, joists & fasteners from deck size.
Concrete & Masonry
6 TOOLSVolume, rebar, block, brick, and mortar takeoffs.
- CONCConcrete Volume CalculatorYards for slabs, footings & columns, with bags.
- REBRRebar Weight & Spacing CalculatorBar count, length & weight from grid spacing.
- CMUBlock / CMU CalculatorBlock count, courses & mortar for a wall.
- BRCKBrick CalculatorBrick count & mortar from wall area and size.
- MRTRMortar & Grout CalculatorBags of mortar or grout for block & cell fill.
- FOOTFooting CalculatorVolume & rebar for continuous and pad footings.
Earthwork & Site
6 TOOLSExcavation, cut & fill, trenching, and aggregate.
- EXCVExcavation Volume CalculatorBank yards from area & depth, with swell.
- C/FCut & Fill CalculatorNet import / export from average cut & fill.
- TRCHTrench Volume CalculatorSpoil, bedding & backfill for a trench run.
- AGGAggregate & Gravel TonnageTons of gravel, sand or base from area & depth.
- CMPTCompaction CalculatorLoose vs. compacted volume and lift counts.
- SWELSoil Swell & Shrink CalculatorBank, loose & compacted volume conversions.
Roofing & Exterior
6 TOOLSRoof area, pitch, shingles, panels, and gutters.
- AREARoof Area & Pitch CalculatorTrue area & squares from footprint and pitch.
- SHGLShingle & Bundle CalculatorBundles & squares, plus starter and ridge.
- PTCHRoof Pitch MultiplierPitch to angle, slope factor & multiplier.
- UNDRUnderlayment CalculatorRolls of felt or synthetic from area & overlap.
- PNLMetal Roofing Panel CalculatorPanels & lineal feet from roof and panel width.
- GUTRGutter & Downspout CalculatorGutter feet & downspouts from drainage area.
Drywall, Paint & Finishes
6 TOOLSDrywall, paint, tile, flooring, and insulation.
- DRYDrywall Sheet CalculatorSheets, screws & tape from wall & ceiling area.
- PNTPaint Coverage CalculatorGallons per coat from area and spread rate.
- MUDJoint Compound CalculatorMud boxes & tape footage by finish level.
- TILETile CalculatorTile count, thinset & grout from area and waste.
- FLRFlooring CalculatorBoxes & underlayment from room area and waste.
- RInsulation CalculatorBatts or blown bags from area and R-value.
General & Shared
7 TOOLSCross-trade field math, takeoffs, and estimating helpers.
- YD³Construction CalculatorConcrete yards, aggregate tons & unit conversions.
- FT²Square Footage CalculatorArea & perimeter with multi-room totals.
- 3·4·5Right-Angle (3-4-5) CalculatorDiagonals & hypotenuse to square up corners.
- %Slope & Grade Calculator% grade, ratio, degrees & rise/run conversions.
- %↑Markup & Margin CalculatorMarkup vs. margin & price to a target profit.
- HRSLabor & Crew Cost EstimatorBurdened crew cost per hour and per day.
- FUELEquipment Fuel Cost CalculatorFuel burn & cost by machine and run hours.
Market Data
3 TOOLSLive-ish prices and trends for the materials you buy.
ABOUT THESE TOOLS
Right-sized HVAC starts with the load and flows downstream: the load sets the BTUs, the BTUs set the airflow, and the airflow sets the duct. These calculators follow that chain — a quick heating and cooling load from area, climate, and construction; required CFM from room volume and target air changes per hour; round and rectangular duct sizes from CFM and friction rate; BTU-to-tonnage conversion for equipment selection; total external static pressure from duct, coil, and filter losses; and the extra refrigerant charge for line sets longer than the factory pre-charge.
The industry-standard methods here are ACCA Manual J for residential loads, Manual S for equipment selection, and Manual D for duct design, with SMACNA standards governing duct construction and ASHRAE 62.1 and the International Mechanical Code setting ventilation requirements. These tools give fast, field-usable numbers in that framework — good for sanity checks, service calls, and preliminary sizing — while a full Manual J remains the right basis for a permit set. Free, in the browser, no account needed.
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