Trades calculators
Trade work runs on a handful of numbers checked over and over: how full a conduit can get, how much fall a drain needs, how big a duct must be for the airflow, the length of a rafter, the spindle speed for a cutter. These calculators do that arithmetic the way it is taught in apprenticeships and trade references, and show every step so you can check it on the job.
They are aids, not authorities. Local codes, the equipment manufacturer's specifications and the inspector have the final word, and electrical, gas and structural work should be done or signed off by a licensed professional.
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- AC Sizing CalculatorGet a rough idea of what size air conditioner you need, in BTU/h and tons. It uses your floor area, sun, number of people and whether there's a kitchen.
- Air Changes per Hour CalculatorFind how many times an hour a fan or purifier changes a room's air (ACH), or the airflow (CFM) needed to reach a target.
- Beam Deflection CalculatorEstimate how far a beam sags, its bending moment and its support reactions. Works for a beam on two supports or fixed at one end, under a point or even load.
- Bolt Circle CalculatorGet the X and Y position of every hole in a bolt circle, ready to drill, from its diameter, number of holes, first-hole angle and center.
- Bolt Torque CalculatorEstimate how much torque to tighten a bolt to for the clamp load you want, using T = K × D × F. Enter the clamp load, or set it as a percentage of proof load.
- Box Fill CalculatorAdd up the volume an electrical box needs for its wires, grounds, devices and clamps, and check it against the box's marked volume.
- Breaker Size CalculatorFind the smallest breaker rating a long-running or short-running load needs under the NEC 125% rule, and the next standard breaker size.
- CFM CalculatorWork out how much airflow, in cubic feet per minute, a room or system needs. Start from the room size and air changes per hour, or from the heat load and temperature difference.
- Compression Ratio CalculatorFind an engine's static compression ratio from the bore, stroke, combustion chamber, head gasket, deck clearance and piston dish or dome volume.
- Conduit Bending CalculatorFind where to mark conduit for offsets, 90° stub-ups, back-to-back bends and 3-point saddles, with the offset multiplier and shrink worked out.
- Conduit Fill CalculatorCheck how full a run of EMT or PVC conduit is, from the size and number of THHN wires inside it, against the 53/31/40% fill limits.
- Crown Molding CalculatorGet the miter and bevel saw settings for cutting crown molding flat on a compound miter saw, for any spring angle and any corner.
- Duct Size CalculatorFind what size round or rectangular air duct you need for your airflow, at a target air speed or friction rate. It also converts between round and rectangular ducts with the Huebscher formula.
- Engine Displacement CalculatorFind engine displacement in cubic centimeters, liters and cubic inches from the bore, stroke and number of cylinders.
- Friction Loss CalculatorFind how much water pressure a pipe run loses to friction, using the Hazen–Williams or Darcy–Weisbach method.
- Heat Loss CalculatorEstimate how fast your home loses heat on the coldest days, through walls, windows, ceiling, floor and air leaks, and the furnace size that covers it.
- Miter Angle CalculatorFind the miter saw setting for a frame or shape with any number of sides or any corner angle. Get the bevel too when the sides lean outward.
- Mortar CalculatorCount the bags of premixed mortar needed to lay a given number of bricks and concrete blocks, using the yield per bag and a waste allowance.
- Pipe Flow CalculatorFind how fast water moves in a pipe, how much a pipe carries, or what size you need, with standard copper, PEX, PVC and steel sizes.
- Pipe Slope CalculatorWork out how much a drain pipe drops over a run at a given slope, or the slope from a measured drop. See it in inches per foot, percent and ratio.
- Pipe Volume CalculatorFind how many gallons or litres of water a run of copper, PEX, PVC or steel pipe holds, from its trade size or inside diameter and length.
- Rafter Length CalculatorLay out a common rafter from the run and pitch. Get its length with the ridge reduction and overhang, the cut angles, and the birdsmouth notch size.
- Speeds and Feeds CalculatorFind how fast to spin a cutter (spindle rpm) and how fast to feed it, for milling, drilling and turning.
- Stress and Strain CalculatorFind the stress, strain and stiffness (Young's modulus) of a bar from a pull test, or how far a bar stretches under a load.
- Tap Drill CalculatorFind the tap drill size for UNC, UNF and metric threads at any percentage of thread, with the nearest standard drill and the thread it leaves.
- Taper CalculatorWork out taper per foot or per inch, the included and half angles, the taper ratio and the tailstock offset from a taper's diameters and length.
- Voltage Drop CalculatorEstimate the voltage lost along a copper or aluminum wire run from its gauge or area, length and current.
- Water Heater Size CalculatorSize a tank water heater from your busiest hour of hot water use. Or size a tankless one from the flow and temperature rise you need.
- Weld Heat Input CalculatorFind arc energy and heat input in kJ/in or kJ/mm from arc voltage, current and travel speed, with the heat efficiency factor for each welding process.
- Weld Metal Weight CalculatorEstimate how much metal a fillet or groove weld holds, from its shape and length, and how much filler wire or rod to buy.
- Wire Gauge CalculatorLook up the diameter, area and resistance of any AWG wire size, or find the nearest gauge for a wire you've measured.