100% free interior design calculators

Free interior design calculators for rooms that fit, flow, and feel right.

Make confident design decisions with practical calculators for rug sizes, furniture clearances, TV viewing distance, room lighting, art placement, curtains, and color. Every DID tool is 100% free to use and gives you an instant, measurement-based result.

Explore free calculators How DID calculates
  • 9interior design calculators
  • 100%free to use
  • Instantresults in your browser

The full toolset

Grouped by the job to be done. Every tool runs instantly in your browser.

Space Planning

Rug Size Finder Find the ideal standard rug footprint (8×10, 9×12 and more) from your room dimensions and furniture layout. Open tool → Furniture Clearance Check walkways and pinch points against the mandatory 30-inch clearance path for comfortable, code-friendly circulation. Open tool → TV Viewing Distance Use SMPTE & THX field-of-view math to size your TV and set the perfect wall-mount height. Open tool →

Lighting

Room Lumens Calculate exact LED lumen demand and foot-candle targets for any room type and activity. Open tool → Recessed Lighting Determine symmetrical can-light spacing and wall offsets for even, clean ceiling layouts. Open tool →

Wall & Art

Gallery Wall Spacer Get fraction-of-an-inch spacing and center lines for a balanced, professional gallery wall. Open tool → Art Hanging Height Enforce the universal 57-inch museum center line and get the exact hook height for any frame. Open tool →

Color & Windows

Curtain Length Compute drapery length and rod height that visually maximize ceiling height, with a live preview. Open tool → 60-30-10 Color Split a room’s surface area into balanced dominant (60%), secondary (30%) and accent (10%) color zones. Open tool →

Built on published standards, not guesswork

Each calculator cites the rule it enforces - the 30-inch clearance minimum, the 57-inch museum center line, THX/SMPTE viewing angles, IES foot-candle targets and the 60-30-10 color proportion. Read the methodology on every tool page.

  • Transparent formulas & sources
  • Accessible (WCAG 2.2) & keyboard-friendly
  • No data leaves your browser