Free Online Tools for Everything You Do
Browse 2,706+ free interactive tools - home improvement estimators, pet calculators, cooking converters, automotive tools, finance planners, fitness calculators, developer utilities and more. No sign-up. 100% private. Runs entirely in your browser.
Circumscribed Circle Calculator — Triangle Circumcircle | nrtechstudio.com
Compute circumradius R = abc/4K, diameter, circumcircle area, and triangle circumcenter from 3 sides or 3 coordinate points. Free, with SVG diagram and verified examples.
Free Citation Generator — APA 7th, MLA 9th & Chicago 17th | nrtechstudio.com
Free citation generator: create APA 7th, MLA 9th and Chicago 17th citations side-by-side for books, journal articles, websites, YouTube videos and newspapers. No signup, no ads, 100% private — everything runs in your browser.
CIWA-Ar Alcohol Withdrawal Score Calculator | nrtechstudio
Free CIWA-Ar (Clinical Institute Withdrawal Assessment for Alcohol, revised) calculator: score all 10 items, total 0–67, and see the severity band wit
Classroom Timer Suite — Visual Countdown, Interval & Noise Meter
Free online classroom timer: visual countdown, stopwatch, interval & Pomodoro timers, classroom noise meter, animated themes (bubbles, bouncing balls, calm), fullscreen projector mode, activity presets and timer queue. No sign-up.
Clay Amount Calculator — How Much Clay Do I Need? (Mug, Bowl, Plate, Vase)
Free clay amount calculator for potters: how much clay do you need to throw a mug, bowl, plate, or vase? Batch mode for multiple pieces, wet vs dry weight converter, trimming waste allowance, and a class/workshop project planner. 100% client-side.
Clay Shrinkage Calculator — Fired Size, Rate & Stage Breakdown | nrtechstudio.com
Free clay shrinkage calculator for potters: predict fired size from greenware, get the greenware size for a target fired dimension (reverse mode), compute shrinkage rate from two measurements, and compound multi-stage shrinkage (wet → bone-dry → bisque → glaze-fired). Metric/imperial. 100% private —
Cleaning Cost Calculator
Free cleaning cost calculator: house cleaning price estimator for homeowners and quote builder for cleaning businesses.
Climbing Fall Factor & Impact Force Lab — Fall Factor Calculator (kN)
Free interactive climbing fall-factor lab: fall factor solver, impact force calculator in kN (UIAA/Goldstone equation), gear kN rating checker, rope elongation database, via ferrata mode and anchor force estimator.
Climbing Grade Converter — YDS, French, V-Scale, UIAA + 18 More Systems
Free climbing grade converter across 22 grading systems: YDS, French, UIAA, British E-grade, Ewbank, V-scale, Font, Dankyu, Peak B, Cracow, aid, ice, mixed & alpine. Full comparison tables with confidence labels. 100% private — runs in your browser.
Clomid Ovulation Calculator — Estimate Ovulation on Clomiphene
Free Clomid ovulation calculator: enter your last period date, the cycle day you started Clomid, and cycle length to estimate your ovulation window (typically 5-9 days after the last tablet), fertile window, and monitoring plan. Educational estimate only — not medical advice.
Tool - Closest Fraction Calculator
Precision decimal to closest fraction calculator for tape measure, machinist tolerances, ruler inches, centimeter conversions, and Farey sequence approximations.
Closet Size Calculator: Reach-In & Walk-In Dimensions, Rod Heights | nrtechstudio
Closet size calculator: reach-in & walk-in dimensions, the 24-inch depth rule, 40/80-inch double-hang rod heights, linear feet of hanging space. Free.
Cloud Base Calculator - Estimate LCL (Cloud Base) Height
Free cloud base calculator: estimate lifting condensation level (LCL) from air temperature and dew point — in meters and feet. Includes inverse mode from an observed cloud base.
CLTV (Customer Lifetime Value) Calculator — Calculate Customer Lifetime Value
Free CLTV (Customer Lifetime Value) calculator: compute base customer lifetime value, margin-based value, the LTV:CAC ratio, and compare 2 customer segments. 100% runs in the browser.
Cm to Km Conversion: Free Centimeters to Kilometers Calculator
Free cm to km conversion tool. Convert centimeters to kilometers and kilometers to centimeters instantly, with a full cm to km conversion chart, the formula, and answers to common questions. 100% client-side.
Cm to M Converter: Convert Centimeters to Meters Online
Free cm to m converter with two-way real-time conversion. Convert cm to meters and meters to cm, browse the cm to m chart, and get quick answers for common cm to m conversions.
Cm to Mm Conversion: Centimeters to Millimeters Calculator
Free cm to mm conversion calculator. Convert centimeters to millimeters and back instantly: 1 cm = 10 mm. Includes quick conversion table, formula, and worked examples for engineering, printing, and schoolwork.
CMYK Code & Universal Color Converter
Interactive CMYK color code converter, RGBA colour picker, RGB to HEX, HSV, HSL, decimal, and RAL color conversion tool.
CMYK to HEX Color Converter Online
Free online CMYK to HEX color converter, CMYK to RGB calculator, and Pantone color converter CMYK. Transform RGB to CMYK, translate RGB to CMYK, and find hex to cmyk colour converter.
CMYK to RGB Converter — Convert CMYK to RGB + HEX | nrtechstudio
Free CMYK to RGB converter: enter C, M, Y, K percentages and get RGB (0-255), HEX code, live color preview, and a step-by-step formula breakdown. Client-side, no uploads.
CO2 Grow Room Calculator — Dose, Flow Rate & Tank Duration
Free CO2 grow room calculator: room volume to CO2 dose (lb, ft³, grams), sealed-room flow rate (CFH), time to target ppm, tank duration, and vented-room injection rate.
COBRA vs Marketplace Calculator — 18-Month Cost Comparison | nrtechstudio.com
Compare COBRA vs Marketplace (Obamacare) health insurance costs over 18 months. Includes premium tax credit estimator, deductible modeling, break-even analysis, and month-by-month chart. Free, private, no signup.
Code Converters Master Hub
Interactive master directory and multi-language code conversion hub across JSON, SQL, TypeScript, Python, Go, and C.
Code Diff
Code Formatter
Code Translator
Coded Message Generator
High-performance secret message coder and decoder supporting Caesar, ROT13, Vigenere, Atbash, Binary, and Hex ciphers.
Friction Coefficient Calculator (μ) — Static, Kinetic & Slip Angle
Free friction coefficient calculator: μ = F/N, friction force from μ, normal force from μ, incline slip angle μ_s = tan θ, plus static & kinetic μ table for 8 material pairs.
Coffee Brew Ratio Calculator — All Methods, Timer & Batch Scaler
Free coffee-to-water ratio calculator with presets for V60, Chemex, French Press, AeroPress, Moka Pot, Espresso & Cold Brew. Includes step-by-step brew timer, batch scaler, and unit converter. 100% client-side.
Coffee Table Size Calculator — Find the Perfect Table for Your Sofa
Find the perfect coffee table size for your sofa: free calculator for table length, height, round diameter, sectional fit and clearance. Inches + cm.
College Cost Calculator - Net Price Estimator by School
Free college cost calculator: enter any school's sticker price and gift aid to estimate net price per year, 4-year total, out-of-pocket cost, and monthly student loan payments. Compare up to 3 schools side by side.
Color Blindness Simulator
Free color blindness simulator: see colors and images as people with protanopia, deuteranopia, tritanopia and 5 more CVD types see them. Severity slider, image upload, WCAG contrast — 100% client-side.
Color Converter — HEX, RGB, HSL, HSV, CMYK, Lab + Palette & Contrast Checker
Free all-in-one color converter: convert between HEX, RGB, HSL, HSV, CMYK and Lab in both directions, generate palettes (complementary, analogous, triadic), check WCAG contrast, and pick colors from images. 100% client-side.
Color Darkener - Darken HEX, RGB & HSL Colors Online
Darken any hexadecimal, RGB, or HSL color by 0-100% toward black, with live preview, 10-step shade scale, before/after contrast ratio, and one-click copy.
Color Desaturator — Desaturate Colors to Grayscale (Rec.709)
Free color desaturator: desaturate any HEX/RGB/HSL color to grayscale with a 0-100% slider, 4 methods (Rec.709 luminosity, average, lightness, HSL) compared side-by-side, copyable HEX/RGB/HSL output. 100% client-side.
Color Inverter — Invert HEX Colors Online
Free online color inverter: flip any HEX color to its exact opposite with live preview, HEX/RGB/HSL codes, WCAG contrast ratio, one-click copy.
Color Lightener - Lighten HEX, RGB & HSL Colors by Percentage
Free color lightener: lighten any HEX, RGB or HSL color by an exact percentage toward white, with HEX/RGB/HSL output, a 10-step tint scale, before/after preview and WCAG contrast ratios.
Color Mixer
Mix two colors online with a ratio slider, blend modes and linear-light option. 100% client-side.
Color Palette Generator — Harmonious Color Schemes
Free color palette generator: build harmonious schemes from any base color, random palettes with locks, WCAG contrast check, and CSS/Tailwind export. 100% client-side.
Color Saturator — Increase Color Saturation Online
Free color saturator: saturate any HEX/RGB/HSL/HSV color with a 0-100% slider, 3 methods (absolute, additive, relative) compared side-by-side, one-click HEX/RGB/HSL/HSV copy. 100% client-side.
Color Shades Generator & Color Palettes Maker
Professional color palettes generator, tints and shades generator, perchance palette maker, material color palette generator, and CSS color pattern generator online.
Color Tint Generator & Split Complementary Palette
Interactive color tint generator, split complementary color wheel creator, image color palette extractor, and font palette generator.
Colour RGB Values, RGBA Color Picker & Image Eyedropper
Free online colour RGB values inspector and RGBA color picker. Pick colours from images, convert hex code to rgba, rgba to rgb, generate randomized colors, and sample exact hexadecimal values.
Combinations Without Repetition Calculator — nCr, nPr, Stars & Bars (Exact) | nrtechstudio
Free combinations calculator: C(n,r) without repetition, combinations with repetition (stars and bars), permutations P(n,r) and n^r, 4-way compare, show-your-work steps, exact BigInt math for large n. 100% client-side.
Insurance Combined Ratio Calculator — Loss Ratio + Expense Ratio
Compute insurance combined ratio from loss ratio and expense ratio. Includes result interpretation, two-company comparator, and component breakdown. Educational estimate, not financial advice.
Comma Separator Converter
Interactive tool that converts newline column lists into comma-separated text, SQL IN clauses, and custom delimited strings.
Comma Delimited & List to String Converter
Interactive comma delimited formatter, list to string conversion tool, SQL quote wrapper, string to ASCII, and Python text to binary.
Commercial Lease Calculator — NNN vs Gross vs Modified Gross (Free)
Commercial lease calculator: compare gross vs NNN vs modified gross, build escalation schedules, amortize TI allowance, convert $/sqft — free, in-brow
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How to Use the Tools Directory
Every tool is a single interactive page: enter your inputs, get instant results, no account needed. Use the search box (shortcut: press /) to jump straight to a tool, or browse categories when you are exploring. Each card links to the tool's permanent URL, which you can bookmark or share.
Because all computation happens in your browser, the tools are fast, private, and free forever. If a result looks wrong, use the one-click report control on the tool page so it can be fixed.
Tool Categories at a Glance
| Category | What you will find | Example tasks |
|---|---|---|
| Developer | Encoders, formatters, regex, network tools | Format JSON, test regex, subnet a network |
| Finance | Tax, loans, salary, investing | Estimate tax brackets, amortize a loan |
| Home improvement | Estimators, measurements, materials | Size a wire, estimate paint or flooring |
| Health & fitness | Body metrics, nutrition, workouts | Track BMI, plan calories, score fitness tests |
| Math & science | Converters, geometry, statistics | Convert units, solve triangles |
| Text | Counters, sorters, generators | Count words, alphabetize a list |
| Color | Pickers, converters, checkers | Convert HEX to RGB, check contrast |
| Everyday life | Cooking, travel, automotive, pets | Convert recipes, plan fuel costs |
Popular Tasks and Where to Start
| I want to... | Start with | Why |
|---|---|---|
| Convert between number bases | Binary Converter | Step-by-step base conversion with charts |
| Validate and format data | JSON Formatter | Pretty-print and check JSON instantly |
| Count words for an essay | Word Counter | Words, characters, reading time |
| Check password strength | Password Strength Meter | Entropy-based strength scoring |
| Grade text readability | Readability Score | Flesch-Kincaid and grade levels |
| Audit color contrast | Accessibility Checker | WCAG contrast ratios in one click |
Tools Directory FAQ
What is the NRTechStudio tools directory?
It is a free catalog of more than 2,700 interactive web tools: calculators, converters, generators, and checkers for developers, finance, home improvement, health, education, and everyday tasks.
Are all the tools really free?
Yes. Every tool in the directory is free to use with no sign-up, no trial, and no paywall. They run entirely in your browser.
Do I need to create an account?
No. There are no accounts, logins, or subscriptions. Open a tool and use it immediately.
Is my data private when I use these tools?
Yes. The tools are 100% client-side: your inputs are processed by JavaScript in your own browser and never sent to a server.
How do I find the right tool?
Use the search box at the top of the directory (press / to focus it), or browse by category. Every tool card shows a short description of what it computes.
Do the tools work on mobile?
Yes. The directory and the tools use responsive layouts that adapt to phones, tablets, and desktops.
How many tools are there?
The directory holds more than 2,700 tools and grows regularly as new calculators and converters are published.
Can I request a new tool?
Yes. Each tool page has a report/feedback control you can use to request features or new tools; requests help prioritize what gets built next.
Are the tools accurate?
Calculators use published formulas and reference data (tax tables, NEC ampacity, standard conversions). Each tool page documents its method, and issues can be reported in one click for a fix.
Do tools work offline?
Once a tool page has loaded, most tools keep working without a connection because the logic is client-side JavaScript. The directory search needs the page loaded first.
What categories are covered?
Developer utilities, finance and tax, home improvement, health and fitness, math and science, text tools, color tools, networking, education, and everyday life calculators, among others.
Can I bookmark or share a tool?
Yes. Every tool has its own permanent URL under nrtechstudio.com/tools/, which you can bookmark or share directly.
Is there an API for these tools?
The tools are interactive web pages, not API endpoints. The underlying math is plain JavaScript you can inspect in the page source.
Why do some tools show ratings?
Ratings aggregate user feedback to surface the most trusted tools and flag pages that need fixes or better explanations.
How often are new tools added?
New tools are published on a continuous pipeline, prioritized by measured search demand and by user requests from the feedback controls.
Who builds these tools?
NRTechStudio, an independent tools studio focused on free, private, client-side utilities that respect user privacy.