CTR K
Professional mechanical engineering tools

Simple, transparent pricing

Start free. Upgrade when you need more. Cancel any time.

Free

Structural references & GD&T tools

$0forever
Get started free
  • Unit converter & reference library
  • Steel sections calculator
  • GD&T calculator
  • Tolerance stack-up
  • Comparison mode
  • Unlimited calculations
Core

Every engineering calculator

$15/mo
$180/yr · save 21%
  • Everything in Free
  • All 48 engineering calculators
  • AI Engineering Assistant (10 q/hr)
  • Save calculations & history
  • Branded PDF reports
  • Public read-only share links
  • Material database & sensitivity charts
Most Popular
Pro

Calculators + the Design Studio

$29/mo
$348/yr · save 26%
  • Everything in Core
  • Fluid-power, P&ID & electrical schematic editors
  • AI Engineering Assistant (20 q/hr)
  • Cross-tool workflow linking
  • Priority email support
  • Early access to new tools
Expert

API access & professional scale

$49/mo
$588/yr · save 29%
  • Everything in Pro
  • AI Engineering Assistant (50 q/hr)
  • Full REST API access (self-serve keys)
  • CAD add-ins — Fusion, Inventor, SolidWorks (soon)
  • Design history & versioning (soon)
  • Dedicated priority support
Team
5–20 seats
$49/seat/mo
billed annually · volume pricing
Custom setup · pricing via email
  • All 48 calculators + schematic editors
  • Volume pricing vs. individual Expert
  • Priority email support
  • SOONSeat management dashboard
  • SOONShared calculation workspace
Contact sales →
Enterprise
20+ seats
Custom
Volume pricing · On-premise option
  • Unlimited seats
  • SOONSSO / SAML integration
  • SOONCustom tool configuration
  • Dedicated SLA
  • On-premise deployment (on request)
Contact sales →

Frequently asked questions