Construction Calculators — US Standards

Cable Tray Fill Calculator

Check NEC 392.22 cable tray fill for multiconductor and single-conductor cables. Get fill %, pass/fail, and the minimum tray width for ladder, ventilated, and solid-bottom trays. Free, no sign-up.

Box Fill Calculator

Calculate NEC 314.16 box fill from conductors, clamps, support fittings, devices, and grounds. Get the required box volume, fill %, pass/fail, and the minimum box size. Free, no sign-up.

Wire Size & Ampacity Calculator

Find the minimum copper or aluminum wire size for a load using NEC Table 310.16, with 310.15 ambient and conductor-count derating and the 110.14(C) terminal limit. Free, no sign-up.

Conduit Fill Calculator

Size conduit per NEC Chapter 9. Add THHN, XHHW, or other conductors and get the minimum trade size and fill % for EMT, IMC, RMC, PVC, ENT, FMC, and LFMC. Free, no sign-up.

Voltage Drop Calculator

Calculate voltage drop % and the minimum copper or aluminum wire size to stay within the NEC 3% / 5% recommendation, single- or three-phase. Free, no sign-up.

Size a single- or three-phase transformer from load in kVA, kW, or secondary amps. Get the required kVA, the next standard size, primary and secondary full-load amps, and the NEC 450.3(B) primary OCPD. Free, no sign-up.

Motor FLC Calculator

Look up motor full-load current from NEC Table 430.248/430.250, then get the 125% branch-circuit conductor ampacity, the 430.52 maximum protection by device type, and the disconnect rating. Free, no sign-up.

Ground Wire (EGC) Size Calculator

Size the equipment grounding conductor from the breaker or fuse rating using NEC Table 250.122, copper or aluminum, with the 250.122(B) upsize for enlarged conductors. Free, no sign-up.

Solar String Sizing Calculator

Size a PV string per NEC 690.7. Get the maximum and minimum modules per string from module Voc/Vmp, temperature coefficients, your record-low and high design temperatures, and the inverter voltage window. Free, no sign-up.

EV Charger Circuit Calculator

Size a Level 2 EV charger circuit per NEC 625. Get the minimum breaker and copper or aluminum wire from the 125% continuous-load rule, plus charging power in kW and approximate miles added per hour. Free, no sign-up.

PoE Power Budget Calculator

Check a PoE switch power budget per IEEE 802.3af/at/bt. Add powered devices by type and PD class to total the watts drawn, see the utilization and headroom, and confirm the load fits the switch budget and port count. Free, no sign-up.

Fiber Optic Loss Budget Calculator

Calculate a fiber optic link loss budget per TIA-568 and FOA. Add fiber length, connectors, and splices to total the cable plant loss in dB, then compare it to the transceiver power budget for the link margin and pass/fail. Free, no sign-up.

CCTV / NVR Storage Calculator

Calculate CCTV / NVR storage and bandwidth. Add IP cameras by resolution and codec (H.264/H.265) to get the hard drive size in TB for your retention days, plus the total network bandwidth. Free, no sign-up.

CCTV Lens & FOV Calculator

Calculate CCTV camera field of view and DORI distances. Enter sensor format, resolution, and lens focal length to get HFOV/VFOV angles and Detect, Observe, Recognize, and Identify ranges in feet per EN/IEC 62676-4. Free, no sign-up.

Culvert Size Calculator

Size a round culvert with Manning's equation. Get the full-flow capacity in cfs and velocity for a diameter, or the minimum standard pipe size for a design flow — concrete, CMP, or HDPE. Free, no sign-up.

Civil & Construction

Rational Method Calculator

Estimate peak stormwater runoff with the Rational Method, Q = C·i·A. Build a weighted runoff coefficient from multiple surfaces, enter the rainfall intensity and area, and get the peak flow in cfs. Free, no sign-up.

Civil & Construction

Rebar Weight Calculator

Calculate rebar weight from ASTM A615 bar sizes. Add bars by size, length, and quantity to get the total weight in pounds and tons, plus a per-bar breakdown and optional cost. Free, no sign-up.

Steel Weight Calculator

Calculate steel weight for plate, bar, tube, pipe, and angle from dimensions. Add multiple pieces to get the total weight in pounds and tons, with a per-piece breakdown and optional cost. Free, no sign-up.

Concrete Calculator

Calculate concrete for slabs, footings, walls, columns, and sonotubes. Add pours to get total cubic yards, the number of 40/60/80 lb bags, a waste allowance, and ready-mix cost. Free, no sign-up.

Gas Pipe Size Calculator

Size natural gas or propane pipe with the NFPA 54 / IFGC longest-length method. Enter the total BTU load and the longest run to get the minimum Schedule 40 pipe size and its capacity in CFH. Free, no sign-up.

HVAC & Piping

Drainage Fixture Unit (DFU) Calculator

Size sanitary drainage pipe from drainage fixture units. Add fixtures to total the DFU load, then get the minimum building drain, branch, or stack size per IPC Table 710.1. Free, no sign-up.

HVAC & Piping

Drain Slope Calculator

Calculate drain pipe slope for DWV and sewer lines. Find the total fall from a run and pitch, or the slope from a measured drop, and check it against the IPC minimum grade by pipe size. Free, no sign-up.

HVAC & Piping

Cut and Fill Calculator

Calculate cut and fill earthwork volume with the average end area method. Enter cross-section areas along the alignment to get total cut, fill, and the net import or export in cubic yards. Free, no sign-up.

Civil & Construction

Joist Span Calculator

Find the maximum allowable floor or deck joist span from the IRC span tables. Pick species, grade, size, and spacing to get the code max span by joist size and check it against the span you need. Free, no sign-up.

Deck Beam Span Calculator

Size a built-up deck beam from the IRC R507.5 table. Pick the species and the deck joist span it carries to get the maximum span for double and triple 2× beams and the minimum size for your post spacing. Free, no sign-up.

Rafter Span Calculator

Find the maximum horizontal roof rafter span from the IRC R802.4.1 tables. Pick the roof or ground snow load, species, grade, size, and spacing to get the max span by size and the minimum rafter for your roof. Free, no sign-up.

Ceiling Joist Span Calculator

Find the maximum ceiling joist span from the IRC R802.5.1 tables. Pick the attic use, species, grade, size, and spacing to get the max span by size and the minimum joist for your ceiling. Free, no sign-up.

Stair Stringer Calculator

Enter the total rise to get the number of risers, the riser height, tread count, total run, and stringer length, with an IRC R311.7 code check on riser and tread. Free, no sign-up.

Concrete Block (CMU) Calculator

Estimate a CMU wall from its size: block count, mortar (cement + sand), core-fill grout, and rebar for 6, 8, and 12 in units per NCMA TEK 14-13. Subtract openings and add a waste allowance. Free, no sign-up.

Insulation Calculator

Find the DOE-recommended R-value for your climate zone and assembly, then the insulation thickness, blown-in bags or batt area, and cost — attic, wall, and floor per the 2021 IECC. Free, no sign-up.

Mortar Calculator

Estimate mortar for brick and block: bags of premixed mortar, or masonry cement and sand, by unit count or wall area. Includes Type N, S, M, O mix ratios per ASTM C270. Free, no sign-up.

Stucco Calculator

Estimate 3-coat stucco: bags of scratch, brown, and finish coat, or field-mixed cement and sand, from your wall area. Per ASTM C926 / SMA thicknesses. Free, no sign-up.

Drywall Calculator

Estimate drywall: sheets, screws, joint tape, and joint compound (mud) from your area or room size. Pick 4×8, 4×10, or 4×12 panels with a waste allowance. Free, no sign-up.

Labor Burden Calculator

Calculate the fully burdened labor rate for construction. Add payroll taxes (FICA, FUTA, SUTA), workers' comp, insurance, and benefits to a base wage to get the labor burden % and the true cost per productive hour for accurate bids. Free, no sign-up.

Man-Hours Calculator

Estimate construction labor man-hours, crew duration, and cost. Enter a quantity and a production rate or labor unit, your crew size, and a productivity factor to get total man-hours, work days, and labor cost. Free, no sign-up.

Retainage Calculator

Calculate construction retainage and your net progress payment. Enter the contract amount, percent complete, and retainage rate — with optional tiered reduction — to get the amount withheld, the net payment due this period, and the cumulative retainage held. Free, no sign-up.

Change Order Calculator

Price a construction change order with overhead, profit, and bond markup. Add labor, material, equipment, and subcontractor costs to get the total price, the markup added, and the true margin vs markup. Free, no sign-up.

Prevailing Wage Calculator (Davis-Bacon)

Calculate the Davis-Bacon prevailing wage. Enter the base rate and required fringe to get the total wage package, the fringe credit from the benefits you provide, the cash due in lieu, and the overtime rate. Free, no sign-up.

Equipment Rent vs Buy Calculator

Decide whether to rent or buy construction equipment. Compare the annual cost of ownership against rental rates to get the break-even utilization, your monthly cost either way, and a clear buy-or-rent recommendation. Free, no sign-up.