Free engineering calculators — built for licensed PEs.

Every calculation prints with a built-in PE stamp + signature block, ready for sealed submittals. Every tool shows the formula being applied, names every variable, cites a source, and supports both Imperial and SI units. Organized by PE discipline. No login, no paywall. Built for working Professional Engineers, not for FE prep.

Hydraulics & Water Resources

Manning's Equation

Open-channel flow: Q from n, A, R_h, S

Darcy-Weisbach

Pipe head loss with Swamee-Jain f

Hazen-Williams

Water-distribution head loss

Reynolds Number

Flow regime: laminar / transitional / turbulent

Triangular weir, low-flow measurement

Orifice Flow

Q = C_d · A · √(2gh)

Time of Concentration

SCS / TR-55 runoff depth and volume

Culvert Hydraulics

FHWA HDS-5 inlet + outlet control

Linear Interpolator

Two-point + table; lin/log; inverse

Dam Safety — landing page

Reservoir Routing

Modified Puls / Storage-Indication level-pool routing

Ogee Spillway

Q = C·L·H_e^3/2, USACE EM 1110-2-1603

Drop Spillway

NRCS NEH-11 straight-drop principal spillway

Stepped Spillway

Energy dissipation, Chanson skimming-flow regime

Hydraulic Jump & Stilling Basin

Conjugate depth + USBR Type II/III/IV

Embankment Seepage

Casagrande phreatic line + Darcy seepage Q

Filter Criteria

Sherard / NRCS D₁₅/D₈₅ ratios

Riprap Sizing

USACE EM 1110-2-1601 D₃₀; Isbash D₅₀

Wave Runup & Freeboard

Wind setup + significant wave + Saville runup

Gravity Dam Stability

FoS overturning, sliding, base pressure with uplift

Dam Breach Peak Discharge

Froehlich 2008 + Xu-Zhang + MacDonald

Hazard Classification

FEMA P-94 low / significant / high screener

Inflow Design Flood (IDF)

% PMF by hazard class — FERC, FEMA, USACE

Environmental Engineering

BOD Removal

First-order kinetics, CSTR/PFR

MLSS & F:M Ratio

Activated sludge loading and SRT

Aeration Tank Sizing

Activated-sludge basin volume

Oxygen Transfer

SOTR ↔ AOTR with α, β, F

Settling Velocity

Stokes / transition / Newton regimes

Chlorine CT Disinfection

EPA SWTR Giardia / virus log inactivation

Lift Station Sizing

Wet well volume + cycle time

Hydraulic Detention Time

HRT and clarifier OFR

Geotechnical Engineering

Terzaghi Bearing Capacity

Strip / square / circular footing

Lateral Earth Pressure

Rankine K_a, K₀, K_p

Slope Stability FoS

Infinite slope, c-φ, with seepage

Consolidation Settlement

1-D primary settlement, NC + OC paths

Pile Capacity

α/β methods, axial single pile

Structural Engineering

Beam Deflection

SS & cantilever, point + UDL

Euler Buckling

Column P_cr, end conditions

Section Properties

A, I, S, r, Z — common shapes

AISC Allowable Stress

ASD tension, compression, flexure

AISC LRFD Steel Design

Design strength φP_n — tension, compression, flexure

RC Beam Flexure

ACI 318 Whitney block, φM_n

Transportation Engineering

Stopping Sight Distance

AASHTO SSD with grade correction

Vertical Curve

Crest & sag K-factor, low/high point

Horizontal Curve

R, D, T, L, M, E geometry

Superelevation

AASHTO e + f, min radius

Mechanical / HVAC Engineering

Pump BHP

Hydraulic, brake, motor power

Fan Affinity Laws

Speed / diameter / density scaling

Duct Pressure Loss

Round / rectangular, Darcy-Weisbach

Heat Exchanger LMTD

Counterflow, parallel, F factor

Psychrometric Load

Sensible & latent HVAC loads

Electrical Engineering

Voltage Drop

NEC AC voltage drop, Cu and Al

Three-Phase Power

kW, kVA, kVAR, PF correction

Motor FLA

Full-load amps, NEC 430.250

Transformer Sizing

kVA from connected load + DF

NEC Conduit Fill

Chapter 9 Tables 1, 4, 5

Chemical & Thermo Engineering

Ideal Gas Law

PV = nRT, with Z-factor

Antoine Vapor Pressure

P_sat from T, common compounds

CSTR / PFR Sizing

Reactor volume, 1st & 2nd order

Carnot & Refrigeration COP

Power cycle & refrigeration efficiency

Field / Astronomy

Eclipse Sun Position

Sun alt/az + path-of-totality check for photographers (Aug 2026 default)

In Development

Fire Protection

Sprinkler hydraulics, hydrant flow

Industrial & Systems

Queueing, reliability, layout

Naval Architecture & Marine

Buoyancy, hydrostatics, stability

Petroleum

Reservoir, drilling, production

Mining & Underground

Stope design, blast, ventilation

Nuclear

Neutronics, shielding, decay heat

Metallurgical & Materials

Fatigue, fracture, phase diagrams

Software

Algorithm complexity, queueing

Architectural

Lighting, acoustics, energy modeling

Agricultural & Biological

Irrigation, machinery, biomass

Free reference cards — all reference cards

Single-page printable cheat sheets for values engineers look up over and over. Browse all reference cards →

Manning's n

Roughness coefficient — concrete to natural streams to floodplains

Hazen-Williams C

Pipe roughness for water mains — new vs. aged values

Runoff Coefficients (C)

Rational Method C by land use, surface, slope, frequency

Curve Numbers (CN)

NRCS / TR-55 CN by land use & hydrologic soil group, with HSG & ARC

Weir Coefficients (C_d)

Sharp-crested, broad-crested, V-notch, ogee, Cipolletti

T_c Methods Compared

Kirpich vs. NRCS Lag vs. TR-55 segmental vs. FAA

Minor Loss Coefficients (K)

Fittings, valves, bends, entrances & exits — h = K·V²/2g

Pipe Roughness (ε)

Absolute roughness by material for Darcy-Weisbach / Moody

Culvert Entrance Loss (K_e)

HDS-5 inlet coefficients — concrete pipe, CMP, box culvert

SCS Storm Distributions

Type I, IA, II, III 24-hr curves & where each applies

Open Channel Geometry

A, P, R, T formulas by shape + best hydraulic section

Orifice Coefficients (C_d)

Outlet & riser Cd — Q = Cd·A·√(2gh)

Hydraulic Jump

Froude, sequent depth, energy loss, jump types

Riprap Sizing

Isbash / HEC-11 D50, gradation, thickness, filter

Specific Energy & Critical Depth

E = y + V²/2g, critical depth, alternate depths

Storm Sewer Design Criteria

Velocity, slope, n, pipe size, cover, full-flow capacity

Stokes Settling Velocity

Particle settling, overflow rate, Type I settling

Reynolds Number Regimes

Laminar/turbulent thresholds + water viscosity

Worked examples — all examples

Long-form design walkthroughs that thread multiple PE-Calc tools end-to-end on real-world problems. Browse all worked examples →

Driveway Culvert (25-yr Storm)

Tc → Rational → HDS-5 → outlet velocity check, with the gotchas called out

24-inch RCP Partial Flow

Circular-pipe geometry, y/D iteration, self-cleansing velocity check

Commercial Parking Lot

Composite C, TR-55 Tc, 10-yr peak Q, first-pass inlet layout

Composite Curve Number

Area-weight CN (not Q), 2.5-in storm runoff depth and volume

6-inch PVC Water Main

Hazen-Williams head loss, minor losses, residual pressure check

36-inch CMP Road Crossing

HDS-5 inlet vs outlet control, HW/D limit, outlet riprap

Photo-Sieve Grain Size

113 grains segmented from a coarse-sand photo; D₅₀ = 1.68 mm, σ = 0.54 φ

CAD & survey automation — paid desktop tools

Separate from the free browser calculators above: downloadable macro kits for your CAD station, built from the same production tooling. Plain source you can read and modify — no DLLs.

OpenRoads Field Kit ↗

25 VBA macros for OpenRoads Designer / MicroStation — parcel labels, PNEZD, COGO, levels. $59

C3D Field Kit ↗

26 AutoLISP commands for AutoCAD Civil 3D — bearings tables, N/E coords, plot-all-PDF. $59

Why another engineering calculator site?

Most existing options bury the math behind ads, leave you guessing what coefficients they're using, or were built for an undergraduate thermodynamics class twenty years ago and never updated. Every PE-Calc tool shows the formula, names every variable, cites a reference, and lets you hand-check the result. The calculators run entirely in your browser — nothing leaves your machine. Both Imperial and SI units on every relevant tool, because real engineering happens in both.

Built for sealed submittals

Every tool's print layout includes a designated PE stamp area, signature line, license number, state, date, and project / sheet field — formatted to slot into a sealed engineering submittal. Hit "Print with PE stamp box" on any tool and you get a clean letter-size calculation sheet with the math, the inputs, the result, the cited reference, and a stamp block ready for your seal and signature. Other calculator sites print a screenshot of an ad-cluttered web page; PE-Calc prints engineering documentation.

What's coming next

New tools are added every week. The disciplines marked "in development" above will populate over coming months. Have a calculator you'd like to see prioritized? Subscribe to the newsletter below and reply to any issue — tool requests are welcome.