90+ precision calculators for contractors, electricians, machinists, engineers, and builders. Every formula verified. No ads. No sign-up.
Most-Used Calculators
Calculator Categories
Construction Calculators
From footing design to finish work: concrete, lumber, roofing, framing, masonry, grading, and site work calculations for residential and commercial construction. Concrete footing, slab, and column calculators; rebar sizing; shingle, tile, and roofing material take-offs; framing calculators for studs, joists, rafters, and trusses; and site calculators for excavation, grading, drainage, and compaction.
Concrete Calculator · Shingle Calculator · Rebar Calculator · Footing Calculator · Lumber Calculator
Electrical Calculators
NEC-based wire sizing, conduit fill, motor current, voltage drop, and load schedule tools for residential, commercial, and industrial electrical work. Calculate ampacity for copper and aluminum conductors; size circuit breakers and fuses; determine conduit fill percentages; calculate motor FLA, LRA, and starting current; size transformers, generators, and battery systems.
Wire Ampacity · Voltage Drop · Conduit Fill · Motor Current · Circuit Breaker
Metal Working Calculators
Precision tools for machinists, fabricators, and tool-and-die makers. Drill speeds and feeds, tap drill sizes, CNC feed rates and chip loads, gear ratios, chain drive lengths, spring rates, taper angles, and sheet metal bend allowances. Covers inch and metric tooling with material-specific SFM for steel, aluminum, stainless, brass, and cast iron.
Drill Speed · Tap Drill Size · CNC Feeds & Speeds · Gear Ratio · Bend Allowance
Engineering & Science Calculators
Applied engineering calculations for structural, mechanical, fluid, and HVAC applications. Beam deflection and bending stress, pipe flow rate and Reynolds number, HVAC tonnage and duct sizing, pump horsepower and head, thermal expansion, centrifugal force, stormwater runoff, and gas law calculations. Reference-quality formulas with source citations.
Beam Deflection · Pipe Flow Rate · HVAC Tonnage · HP & Torque · Reynolds Number
Unit Converters & Trade Tools
Fast unit conversion and trade-specific reference tools. Convert fractions to decimals, AWG wire gauge to mm2, pressure between PSI/bar/kPa, torque between ft-lb and N-m, area, volume, flow rate, and temperature. Includes tape measure conversion, decimal-to-fraction lookup, and hardness scale conversion between Rockwell, Brinell, and Vickers.
Decimal to Tape Measure · Temperature · Fraction to Decimal · Pressure Units · Wire Gauge
Why BuildCalc?
Every calculator uses the same formulas found in the Machinery Handbook, NEC, AISC Steel Manual, and ACI 318. Not dumbed down. Correct.
No account required. No paywalls. Works on any phone or tablet on the job site. Results update instantly as you type.
Every calculator shows its formula and key assumptions. Verify the output against your own reference. We encourage it.
We add new calculators based on what trades actually need. 90+ tools and counting.
Free Online Trade Calculators for Construction, Electrical, and Machining
BuildCalc is a free collection of construction calculators, electrical calculators, machining calculators, and engineering tools designed for working professionals. Whether you are a general contractor estimating concrete for a slab, an electrician sizing wire for a long run, a machinist setting up a CNC program, or an engineer checking beam deflection, BuildCalc has the calculation you need, instantly, with no ads or sign-up required.
Our construction calculators cover the full project lifecycle: from excavation and footing design through framing, roofing, insulation, siding, and finish work. Input your dimensions and get material quantities, weights, and costs in seconds. Every calculator shows its underlying formula so you can verify results against your own code references.
The electrical section includes NEC-compliant wire ampacity tables, voltage drop calculators, conduit fill calculators, motor sizing tools, transformer KVA calculators, and battery runtime calculators. Calculations follow NEC Article 310 and standard engineering practice for 120V, 240V, and 480V single and three-phase systems.
Machinists and fabricators will find drill speed and feed rate calculators, CNC feeds and speeds calculators, tap drill size charts, gear ratio calculators, chain drive calculators, spring rate calculators, bend allowance calculators, and metal weight calculators. Our engineering calculators cover beam deflection, pipe flow, HVAC load sizing, pump horsepower, thermal expansion, Reynolds number, and stormwater runoff using the Rational Method.
All calculators are free to use, run entirely in your browser, and work on any device. No data is sent to our servers. Bookmark the ones you use most or browse by category to discover a new tool that saves you time on the next job.