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Engineering

Browse 100 Reddit-sourced calculators, estimators, validators, and converters across electrical, mechanical, civil, fluid-thermal, materials, structural, plumbing, safety, surveying, and engineering-conversion trades.

107 tools available

Sub-categories

Electrical
Wire, conduit, voltage drop, and code math for sparkies, low-voltage technicians, and apprentices.
Mechanical
Beams, motors, hydraulics, gears, and torque for designers, technicians, and field engineers.
Civil
Earthwork, drainage, surveying, and foundation sizing for civil engineers, surveyors, and sitework contractors.
Fluid & Thermal
Duct, pipe, refrigerant, BTU, and tankless sizing for HVAC and plumbing professionals.
Materials
Drywall, paint, masonry, rebar, lumber, and concrete estimating for builders, estimators, and DIYers.
Engineering Conversions
Engineering-specific unit conversions for torque, stress, flow, viscosity, thermal conductivity, and more.
Structural
Joists, headers, footings, columns, and shear walls for framers, deck builders, and structural designers.
Plumbing
Pipe sizing, water heaters, drainage slope, traps, and rainwater harvesting for plumbers and builders.
Safety & Compliance
Arc flash, fall protection, PPE selection, noise, and confined space checks for jobsite safety pros.
Surveying & GIS
Bearings, traverses, areas, and UTM zone math for surveyors, mappers, and GIS analysts.
Energy & Renewables
Solar payback, ROI, and incentive math for the r/solar, r/OffGrid, r/RenewableEnergy, and r/homeimprovement crowd weighing rooftop PV, batteries, and heat pumps.

Voltage Drop Calculator

Compute the percentage drop across a feeder or branch circuit quickly.

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Wire Size & Ampacity Sizer

Find the conductor and OCPD size for any continuous load.

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Conduit Fill Calculator

Validate raceway fill against the 40% rule and Chapter 9 tables.

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Box Fill Calculator

Size a box to meet NEC 314.16 volume and claw counts.

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Residential Service Load Calculator

Run a quick NEC 220 standard or optional demand factor.

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Conductor Derating & Correction

Combine adjuster factors for one final ampacity.

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Transformer kVA & Buck-Boost Sizer

Pick the right kVA, tap, and configuration for a transformer job.

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Motor FLA & Feeder Sizing (NEC 430)

Compute FLA, feeder ampacity, and OCPD limits.

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Low-Voltage Cable Run Calculator

Estimate end-of-run voltage, signal loss, and gauge upgrades.

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Room Lighting Lumens Calculator

Estimate fixture count and layout for any space.

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Beam Span & Size Estimator

Quick-check a wood, LVL, or W-shape against deflection.

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Spread Footing & Pad Sizer

Estimate a square isolated pad for axial and moment loads.

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Rebar Weight & Length Calculator

Convert bar size, length, and lap into pounds and tons.

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Stair Stringer Calculator

Lay out rise, run, and stringer length to code.

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Motor Horsepower Converter

Convert between mechanical, metric, BTU, and electrical HP.

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Cut/Fill Volume Calculator

Compute net cut and fill volumes with shrink and swell.

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Traverse Closure & Bowditch Adjust

Compute misclosure and adjusted coordinates.

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Horizontal & Vertical Curve Solver

Solve PC, PT, and station offsets for any curve.

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Coordinate Inverse & Forward

Convert between DMS coordinates and azimuth/distance.

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Slope & Grade Calculator

Express slope in pitch, percent, ratio, and angle.

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Culvert & Storm Pipe Sizing

Compute design Q and pipe diameter with Manning's equation.

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Aggregate Tonnage Calculator

Compute cubic yards, tons, and bag counts for any job.

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Manual J Lite Load Calculator

Estimate room-by-room heating and cooling loads.

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Duct Sizing & CFM by Friction

Size duct runs from CFM and friction rate.

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Refrigerant Target Superheat & Subcool

Get the right superheat or subcool target by gas.

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Furnace & AC BTU Sizing

Match a unit's capacity to the home.

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Drywall Sheets, Mud & Screws Estimator

Compute drywall sheets, joint compound, tape, and screws.

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Paint Coverage & Gallon Estimator

Estimate gallons of paint, primer, and prep.

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Board Feet & Lumber Cost

Compute board feet, cost, and fall-off vs. vendor counts.

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Linear Feet vs Board Feet Converter

Convert between BF and LF for any nominal size.

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Compound Miter & Crown Angle Calculator

Get miter and bevel for any crown or picture frame.

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Wood Shrinkage & Movement Calculator

Estimate dimensional change across moisture content.

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Stair Stringer Diagram Generator

Visualize the cut layout and printable diagram.

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Mortar Mix Ratio Calculator

Get Portland, lime, and sand batched by mix type.

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Brick & CMU Block Counter

Estimate brick, block, mortar, and grout.

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CMU Grout Volume Calculator

Estimate grout for bonded or unbonded CMU cells.

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Wall Area & Material Estimator

Compute wall SF net of openings.

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Simple Bar-Chart Schedule Builder

Lay out a small job's milestone Gantt without MS Project.

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Ladder Angle & Pitch Safety Checker

Validate a ladder against OSHA 1910.23.

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Fall Clearance & Anchor Height Calculator

Compute required fall clearance per OSHA.

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Daily Construction Report Builder

Generate a printable site-log from a daily form.

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Bid Markup & Margin Calculator

Compute sell price, gross profit, and tax.

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Labor-Hours Per Task Estimator

Estimate crew days, man-hours, and labor cost.

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OSHA Stair & Guardrail Compliance Checker

Validate stair dimensions and guardrails against OSHA 1910.

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Torque Unit Converter

Switch between Nm, lb-ft, kgf-m, and oz-in.

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Pressure / Stress Converter

Translate Pa, MPa, psi, ksi, bar, and atm.

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Flow Rate Converter

Switch between CFM, m3/s, GPM, and L/min.

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Dynamic & Kinematic Viscosity Converter

Convert cP, mPa-s, cSt, and mm2/s.

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Thermal Conductivity Converter

Translate W/(m K), BTU/(h ft F), and W/(m C).

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Energy Unit Converter (Engineering)

Convert J, kJ, kWh, BTU, therm, and ft-lb.

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Panel Load & Sub-Panel Sizer

Tally a panel's connected load and pick the next standard bus rating.

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Wire DC Resistance Calculator

Compute the ohms and percent drop for any gauge length and material.

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Raceway Fill by Trade Size & Wires

Size EMT, PVC, and flex by actual cable area and Chapter 9 tables.

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Solar PV Wire & String Sizer

Compute conductor ampacity and Voc correction for PV arrays.

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Generator Sizing Calculator

Pick the right standby or jobsite kW for any load list.

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DC Battery Runtime Estimator

Estimate runtime, depth-of-discharge, and battery bank size.

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Gear Ratio & Output RPM

Compute gear train ratios, output RPM, and torque multiplication.

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ASME Shaft Diameter Sizer

Estimate a shaft diameter from torque and material allowable.

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Screw Jack Mechanical Advantage

MA, velocity ratio, and efficiency for a screw jack.

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Two-Pulley RPM & Speed Ratio

Match driver to driven pulley by RPM, diameter, and belt length.

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Spring Rate (k) Calculator

Size a compression or tension spring from load and deflection.

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Open Channel Flow & Manning Velocity

Compute uniform flow for a ditch, swale, or channel cross-section.

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Catch Basin & Inlet Sizing

Sump and grate capacity check against design Q.

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Riprap & Outlet Protection Sizing

Stabilize a culvert outlet with the right stone size.

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Shrink & Swell Bank-to-Compacted Cubic Yards

Convert bank yards to compacted or loose yards using shrink/swell factors.

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Stormwater Detention Volume

Size a detention basin for pre- vs. post-development runoff.

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True ↔ Magnetic Bearing Converter

Convert true azimuth to magnetic with local declination.

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Pipe Schedule ID/OD Lookup

Find inside diameter, wall thickness, and weight per foot for any schedule.

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Boiler Heat Load by EDR

Convert EDR (sq ft) into MBH for steam or hot-water boilers.

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Chilled Water Pipe Sizing

Pick a chilled water pipe by GPM and ΔT with velocity caps.

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Closed-Loop Expansion Tank Sizing

Pick a diaphragm expansion tank for a hydronic or hot-water loop.

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Natural Gas Pipe Sizing (BTU)

Match gas pipe length and BTU load to the right nominal size.

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Concrete Bag Count Calculator

Count 60-lb, 80-lb, or bag-calculator-ready mixes for any pour.

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Stucco & Plaster Coverage Estimator

Coverage, bags, and labor for scratch, brown, and finish coats.

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Roof Shingle Squares Estimator

Count shingle squares, starter, ridge cap, and felt underlayment.

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Ceiling Tile & Grid Estimator

Count 2x2 / 2x4 tiles, grid mains, tees, and wire.

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Fence Material Estimator

Posts, rails, pickets, concrete, and gates for any fence run.

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AWG ↔ mm² Wire Gauge Converter

Convert AWG / kcmil to metric mm² cross-section and diameter.

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Hardness Scale Converter (HRC/HB/HV)

Approximate cross-scale conversions between Rockwell, Brinell, and Vickers.

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Frequency ↔ Wavelength Converter

Convert Hz to wavelength in vacuum, air, or with speed-of-sound.

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Specific Heat Capacity Converter

Convert J/(kg·K), BTU/(lb·°F), and cal/(g·°C).

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Floor & Ceiling Joist Span Estimator

Quick-check a wood joist or TJI against span tables.

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Door / Window Header Beam Sizer

Estimate a header for a door or window opening in a bearing wall.

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Deck Post & Footing Sizer

Sizing for deck posts, footings, and beam spans per IRC.

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Euler Column Buckling Load

Compute critical buckling load for a fixed/pinned steel or wood column.

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Shear Wall Line Length & Capacity

Estimate required shear wall length for a given wind or seismic story shear.

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Tank Water Heater Sizing by Household

Pick a tank size (gal) for a family of 1–6.

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Pipe Flow Velocity & Friction Loss

Solve velocity and Hazen-Williams head loss for any diameter.

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Floor Drain Trap Primer Frequency

Compute primer valve cycles/day to keep P-traps wet.

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Rainwater Harvesting Tank Sizer

Size a cistern from roof catchment area and local rainfall.

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Restaurant Grease Trap Sizer

Pick a grease trap by fixture count and flow rate.

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Arc Flash Boundary (IEEE 1584)

Compute incident energy and arc flash boundary distance.

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Confined Space Air Monitoring Limits

O2, LEL, CO, and H2S atmospheric alarm criteria.

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Lockout / Tagout (LOTO) Procedure Builder

Generate a printable LOTO isolation procedure.

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Noise Dose & TWA Calculator (OSHA / NIOSH)

Compute 8-hour time-weighted average and % dose.

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PPE Category 0–4 Selector (NFPA 70E)

Pick the NFPA 70E PPE category for any arc flash task.

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Bearing (NE/NW/SE/SW) ↔ Azimuth Converter

Convert quadrant bearings to azimuth decimal degrees and back.

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Bowditch / Compass Rule Adjust

Distribute a traverse misclosure by distance.

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UTA / Coordinate Area Calculator

Compute planar area of an ordered lat/lon or N/E polygon.

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UTM Zone Lookup by Longitude

Find the UTM zone, central meridian, and convergence for any longitude.

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Resistor Color-Band Decoder

Read a 4-band or 5-band resistor color code into ohms, with tolerance and ppm/K.

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Solar Payback & ROI

Estimate the payback period, lifetime savings, and IRR of a rooftop solar install.

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Wall Framing Spec Check

Validate a stud-and-plate wall against common code spans.

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Server Room BTU / UPS Sizer

Size a small server closet's cooling and UPS load.

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Windows Custom ISO / WIM Sizer

Estimate the final .iso size for a custom Windows install image.

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IPv6 Subnet Allocator

Determine the right sub-prefix from a /N delegation.

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3-2-1 Backup Cloud TCO

Estimate the monthly cost of a 3-2-1 backup plan with cold-cloud tier.

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