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.
Rolling Resistance Calculator: Force, Power, Incline and Coast-Down
Free rolling resistance calculator: force (F = Crr x m x g), power, hill-climb force, surface comparison, and coast-down distance. Curated Crr presets
Roman to Integer Converter — Convert Roman Numerals to Numbers (Free)
Decode Roman numerals to numbers free: strict validator, step-by-step breakdown, batch mode, and overline (vinculum) support to 3,999,999. 100% private.
Roof Replacement Cost Calculator & Cost Lab 2026 — Estimate by Material, Pitch & Region
Free roof replacement cost calculator: convert footprint to roof squares via pitch factor, compare 9 roofing materials, tear-off layers, regional labor rates, repair-vs-replace check, insurance deductible math and financing payments. 100% client-side estimates.
Rotational Kinetic Energy Calculator: 1/2 I omega^2, 8 Inertia Shapes, RPM Solver | nrtechstudio.com
Free rotational kinetic energy calculator: E = 1/2 I omega^2 with an 8-shape moment of inertia library (cylinder, sphere, rod, hoop, point mass), rad/
Round to the Nearest Cent Calculator — Half-Up & Banker's Rounding
Free rounding calculator: round to the nearest cent, nickel (5 cents), ten, hundred, thousand, or any place value. Half-up and banker's (half-even) methods with step-by-step work.
RSA Calculator – Cryptosystem Encryption & Decryption
Rsa calculator, rsa encryption calculator, rsa encryption decryption, rsa cryptosystem calculator, rsa decryption, rsa cryptography calculator, rsa encryption online, rsa decrypt online, encrypt rsa, rsa tool, rsa encrypt decrypt online.
RSA Key Generator & Public Private Key Pair Inspector
Standalone professional RSA key generator, online RSA encryption keys generator, and OpenSSL key pair creator. Generate RSA key SSH, inspect public RSA key example, and generate public private RSA keys with zero AI slop.
RSS Feed Generator — Create RSS 2.0 XML
Free RSS feed generator — create valid RSS 2.0 XML online with live preview, validation, and one-click download.
Rug Size Calculator — What Size Rug for Living Room, Dining & Bedroom
Free rug size calculator: what size rug for your living room, dining room, bedroom & hallway. Standard-size picker, coverage check, pad sizer + cost.
Rule of Thirds Calculator
Free rule of thirds calculator: compute exact grid points for any image size, preview the 3x3 grid live, overlay it on your photo, and export. 100% client-side.
Running Form Lab — Cadence Stride Length Calculator (Free)
Free running form lab: cadence ↔ stride length solver, stride & cadence targets by height, overstriding risk estimator, running metronome, ground contact time estimator. 100% client-side, no signup.
Running Pace Calculator & Race Time Predictor — VDOT, Riegel & Cameron
Free running pace calculator: predict race times for 5K, 10K, half marathon & marathon with 3 models side-by-side (Riegel, Cameron, Jack Daniels VDOT), plus Daniels training paces, grade-adjusted pace, Boston qualifier checker, age grading & split planner. 100% client-side.
Rust Decay Calculator — Building Decay Time & TC Upkeep Cost
Free Rust decay calculator: building decay times per tier (Twig 1h, Wood 3h, Stone 5h, Sheet Metal 8h, Armoured 12h), Tool Cupboard upkeep cost per 24h with the real progressive tax brackets, and how long your TC stock lasts.
RV Loan Calculator — Payment, Amortization & Affordability
Free RV loan calculator: monthly payment, yearly amortization schedule, affordability (DTI) check, and side-by-side scenario comparison. 100% client-side.
SAE to Metric Calculator — Wrench, Socket & Bolt Size Conversion
Convert SAE (fractional inch) sizes to metric millimeters and back. Wrench/socket interchange chart with fit ratings, SAE bolt diameter + UNC/UNF thread pitch reference, and worked examples. 100% free, runs offline in your browser.
Salary Calculator — Salary to Hourly Pay, Overtime & True Hourly Rate
Free salary to hourly calculator: convert annual salary to hourly wage and back, overtime pay at 1.5x time-and-a-half, your true hourly rate with unpaid overtime and commute, freelance hourly rates, and paycheck estimates. 100% private — runs in your browser.
Salary Inflation
Calculate salary adjusted for inflation by year and convert hourly, monthly, and annual pay rates.
Sales Commission Calculator — Tiered, Accelerator & OTE | nrtechstudio
Free sales commission calculator: graduated & retroactive tiers, accelerators, kickers, quota attainment, splits, clawbacks, draws and OTE. See every step of the math. 100% client-side — your numbers never leave your browser.
Sample YAML File Generator, Formatter & Validator
Free online sample YAML file generator, YAML formatter online, validator, and fixer. Explore YAML examples, Docker/K8s templates, syntax guides, and learn how to write a YAML file.
Sand Calculator | Tons, Cubic Yards & Bags | nrtechstudio
Free sand calculator: estimate sand in cubic yards, tons, and bags for concrete, masonry, fill, play, paver base, and pool filter sand. Metric + imperial.
Sandbox Size Calculator — Sand Volume, Bags, Lumber & Cost
Sandbox size calculator: sand volume in cu ft/cubic yards, 50-lb bag count,
SAPS II Score Calculator — ICU Severity Score + Mortality Estimate
Free SAPS II Score calculator: calculate the Simplified Acute Physiology Score II (Le Gall 1993) from 12 physiologic variables + age + chronic disease + admission type (total 0–163) with a transparent per-variable point breakdown and logistic-regression mortality estimate. Educational tool, not medical advice.
Sauna Size Calculator — Room, Heater kW, Bench, Stones & Vent Planner
Free sauna size calculator: plan room size by bathers, heater kW, bench depth, sauna stones, ventilation, door swing and safety checks — 7 planner mod
Scale Model Lab — Scale Model Conversion Suite (1:72, HO, N, Rescale %, Printable Ruler)
Free scale model conversion suite: real↔model converter with hobby presets (HO 1:87, N 1:160, 1:72, 1:48, 1:35, dollhouse 1:12), what-scale identifier, between-scale rescale %, fractional-inch output, printable scale ruler, model train scale speed, size comparison & paint mixer. 100% client-side.
Schema Generator
Schema Validator
Schengen Visa 90/180 Calculator — Track Your Days & Avoid Overstay
Free Schengen 90/180 rule calculator: log your trips, see days used in the rolling 180-day window, check planned trips, find your max stay date and next safe re-entry. 100% private — runs in your browser.
Sci Calculator
Advanced web-based scientific calculator.
Scientific Calculator for Chemistry & Mass to Volume Studio
Interactive scientific calculator for chemistry, mass to volume conversion calculator, electronic calculator simulator, and statistics suite.
Scientific Calculator Texas Instruments Online & Graphing
Interactive scientific calculator Texas Instruments online, 2D math graphing calculator, and 3D online graphing calculator.
Screen Dimension & Volume Calculator
Aspect ratio finder, screen dimension calculator, volume calculator (rectangular prism, triangular prism, cubic), area calculator, and px-cm converter.
Scuba Air Lab — SAC Rate Calculator, Gas Planning & Tank Guide
Free scuba gas planning suite: SAC rate calculator (metric + imperial), RMV converter, cylinder database (AL80, HP100, LP85, steel 12/15/18L, twinsets), gas planner with rule of thirds, rock-bottom / turn pressure, dive-time estimator and tank fill calculator. 100% client-side, no signup.
Section Modulus Calculator: S=I/c, Bending Stress and Plastic Modulus
Free section modulus calculator: elastic S=I/c and plastic Z for rectangle, circle, hollow tube, I-beam, T-section and channel. Bending stress solver
Tool - See JSON Online Viewer, Formatter & Validator
High-speed online JSON viewer, JSON decoder, tree inspector, UTF-8 validator, and JSON to string code generator.
Segment Area Calculator — Circular Segment Area, Sector, Chord & Arc Length
Free circular segment area calculator: enter radius plus central angle, chord length, or sagitta (segment height) to get segment area, sector area, triangle area, arc length, and a live SVG diagram with step-by-step show-your-work.
Self-Employed Tax Calculator
High-precision 1099 Self-Employed Tax Calculator, Quarterly Estimated Tax, FICA, and State Tax Engine.
Sell-Through Rate Calculator — Unit Terjual vs Received, Multi-SKU & Reorder Planner
Free sell-through rate calculator: % units sold vs received, multi-SKU comparison with slow-mover flags, retail benchmarks & reorder planner.
Selling Leave Days Calculator - Military Leave Sell-Back Payout
Free military leave sell-back calculator: estimate your payout from unused leave days, track the 60-day career limit, and compare selling vs taking leave.
Sentence, Word & Paragraph Counter
Standalone professional sentence counter online, paragraph counter, and word and sentence counting tool. Analyze sentence distribution, count words in paragraph, and calculate number of words in real time.
SEO Checker Tool, HTML Validator & Schema Generator
Free online SEO checker tool, web SEO checker, and SEO validator. Validate HTML online, check SEO meta tags, calculate SEO quality score, and generate structured data with our JSON to schema generator.
SEO Meta Description & Title SERP Simulator
Free online SEO meta description generator and Google SERP simulator. Real-time character and pixel counter for desktop & mobile snippet optimization.
SEO Meta & Title Length Checker
Real-time dual SERP simulator, pixel width analyzer, and SEO title and description length checker.
SEO Title Length – SERP Preview & Meta Tag Checker
SEO title length, meta title length, meta description character limit, seo description length, title tag preview tool, meta title checker, title tag checker, check seo title, title tag meta tag, google meta description length, meta description character count, maximum meta description length, recommended meta title length 60 characters seo, meta desc checker, meta keywords checker, title tag checker tool.
Septic Tank Size Calculator — Code-Based Sizing in Gallons & Litres | nrtechstudio.com
Septic tank size calculator: code-based sizing in gallons and litres from bedrooms or daily flow, plus dimensions, drain field area, and pump-out sche
Series Resistor Calculator (Voltage Divider + LED Helper) — nrtechstudio
Free series resistor calculator: total resistance Rt = R1+R2+..., per-resistor voltage drop Vi = V·Ri/Rt, power Pi = I²·Ri, voltage divider designer (forward + reverse), E12/E24 standard-value picker, and LED series-resistor helper. 100% client-side, no sign-up.
SERP Keyword Checker & Rank Tracker
Interactive SERP keyword checker, SEO rank position analyzer, search results simulator, and CTR curve estimator.
Google SERP Snippet Preview & Simulator
Free online Google SERP simulator to preview how web pages, title tags, and meta descriptions appear in Google search results on desktop and mobile.
Severance Pay Calculator — Estimate Your Package, Taxes & Take-Home Pay
Free severance pay calculator: estimate your severance package from salary and years of service, add unused PTO payout by state law, see the 22% federal withholding estimate and your net take-home pay. Lump-sum vs salary-continuation comparison included.
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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.