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

Explore the toolset

A quick look at the calculators. Every tool runs instantly in your browser — no sign-up.

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 → 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 → Gallery Wall Spacer Get fraction-of-an-inch spacing and center lines for a balanced, professional gallery wall. Open tool →
View all 9 tools

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

Good to know

Frequently asked questions

Everything you might wonder before you start measuring.

Are DID’s interior design calculators really free?

Yes — every tool on DID is 100% free, with no sign-up, no trial, and no paywall. We plan to cover costs with unobtrusive advertising, not by charging you.

Do I need to create an account or install anything?

No. The tools run instantly in your web browser. There is nothing to download, register, or log in to.

How accurate are the results, and what are they based on?

Each calculator implements published design standards — the 30-inch walkway clearance minimum, the 57-inch museum hanging line, SMPTE and THX viewing angles, IES foot-candle targets, and the 60-30-10 color rule. Every tool page states the rule and the math it uses so you can verify it.

Do you store the room dimensions or measurements I enter?

No. All calculations happen locally in your browser with plain JavaScript. Nothing you type is ever sent to us or saved on a server.

What units do the calculators use?

US customary units — inches and feet. The tools are built for a United States audience (en-US) and return imperial measurements.

Do the tools work on my phone?

Yes. The whole site is responsive and keyboard-accessible, and the calculators are designed to work comfortably on small screens.

Can I rely on these results for construction or purchasing decisions?

Treat the results as informed guidance, not professional advice. Always re-measure your own space and consult a licensed designer, electrician, or contractor before buying materials or making structural or electrical changes.

Can I share my results with someone?

Yes. Every tool has a “Copy result link” button that encodes your inputs into the URL, plus one-tap sharing to Pinterest, Facebook, X, WhatsApp, and email.

Do the calculators need an internet connection to work?

Only to load the page. Once a tool is open, the calculations run entirely on your device — no further network requests are needed to get your answer.

Can I request a new tool or report a problem?

Absolutely. We maintain and refine the toolset continuously. Email [email protected] or use our contact page to suggest a calculator or flag an error — we read every message.

Open by principle

Why we value open source

DID is built in the spirit of the open web. We believe the knowledge that makes a home work — clearances, proportions, light levels — belongs to everyone, not locked behind a consultation fee or a proprietary app.

So we build on open-source foundations and open, published standards, we show the exact formula behind every result, and we keep the experience fast, private, and free. Open standards and shared knowledge made these tools possible; giving them back, in the clearest form we can, is how we say thank you.

  • Open standards. SMPTE, THX, IES and the 57-inch museum line — industry knowledge, freely shared.
  • Open methods. Every calculator explains its math so you can check it yourself.
  • Open web. Built with open-source tooling and standards — no heavy trackers, no lock-in.
  • Free access. No paywalls, no sign-ups — useful design math for everyone.