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, Rh, S
Darcy-Weisbach
Pipe head loss with Swamee-Jain f
Hazen-Williams
Water-distribution head loss
Reynolds Number
Flow regime: laminar / transitional / turbulent
Sharp-Crested Weir
Q = C · L · H3/2
Broad-Crested Weir
Spillway / overflow
V-Notch Weir
Triangular weir, low-flow measurement
Orifice Flow
Q = Cd · A · √(2gh)
Time of Concentration
Kirpich + NRCS lag
Rational Method
Peak runoff: Q = CIA
NRCS Curve Number
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·He3/2, 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 Ka, K0, Kp
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 Pcr, end conditions
Section Properties
A, I, S, r, Z — common shapes
AISC Allowable Stress
ASD tension, compression, flexure
RC Beam Flexure
ACI 318 Whitney block, φMn
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
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

Single-page printable cheat sheets for values engineers look up over and over.

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
Weir Coefficients (Cd)
Sharp-crested, broad-crested, V-notch, ogee, Cipolletti
Tc Methods Compared
Kirpich vs. NRCS Lag vs. TR-55 segmental vs. FAA

Worked examples

Long-form design walkthroughs that thread multiple PE-Calc tools end-to-end on real-world problems.

Driveway Culvert (25-yr Storm)
Tc → Rational → HDS-5 → outlet velocity check, with the gotchas called out
Photo-Sieve Grain Size
113 grains segmented from a coarse-sand photo; D₅₀ = 1.68 mm, σ = 0.54 φ

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.

Monthly engineering case studies

One real stormwater or hydraulics design problem per month, with the math worked out and the gotchas called out. No tutorials, no fluff.

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