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.
Spaced Repetition Planner: SM-2 Calculator, Study Schedule Forgetting Curve
Free spaced repetition planner: a verified SM-2 calculator, an exam-date study schedule generator with calendar (.ics) export, and an interactive forgetting curve visualizer. 100% client-side — your data never leaves your browser.
Speaker Placement Calculator — 5.1, 7.1 & Dolby Atmos Layout Planner (Free)
Where should your speakers go? 5.1, 7.1 & Atmos placement angles, distances and room-fit check — free home theater layout calculator.
Specific Gravity Calculator - SG from Density, Weighing and Urine SG
Free specific gravity calculator: SG from density, density from SG, SG by hydrostatic weighing (Archimedes), urine SG interpretation, reference table
Specific Impulse Calculator
Compute specific impulse (Isp) from thrust and mass flow rate, convert Isp to exhaust velocity, calculate total impulse and density impulse. Verified
Speed Converter — MPH, KM/H, M/S, Knots, Mach
Free online speed converter: convert mph, km/h, m/s, knots, ft/s, Mach and fractions of light speed live, with running pace mode and real-world speed comparisons. 100% client-side.
Speed of Light Calculator — c = 299,792,458 m/s
Free speed of light calculator: c = 299,792,458 m/s exact. Convert m/s, km/s, km/h, mph, ft/s, mi/s; time-of-flight Earth–Moon & Sun; c = λν wavelength–frequency solver; light-year distances; refractive slowdown v = c/n.
Speed of Sound Calculator — Air, Altitude, Humidity, Mach Number & Echo Distance
Free speed of sound calculator: c = 20.05√T in air with altitude (ISA) and humidity correction, Mach number, sound speed in water, steel and helium, echo distance d = c·t/2, and a speed unit converter. 100% in-browser, no sign-up.
Speedometer Gear Calculator — Drive & Driven Gear Teeth (Free)
Free speedometer gear calculator: find the correct driven gear teeth from drive teeth, axle ratio and tire revs/mile. Reverse mode shows speedometer error for an installed gear. Includes TCI transmission gear charts. 100% client-side, no signup.
Speeds & Feeds Suite — RPM/SFM, Feed Rate, Chip Load, Tapping, MRR + Power Calculator
Free speeds and feeds calculator suite: RPM/SFM solver, milling & lathe feed rate calculator, material speed database (HSS/carbide/cobalt), chip load advisor, tapping speeds & feeds, MRR + spindle power estimator, and printable reference charts. Imperial + metric.
Sphere Density Calculator — Bulk Density & Packing Density (SC, BCC, FCC, HCP)
Free sphere density calculator with two modes: (1) bulk density of a solid sphere from mass and radius, ρ = m / V with V = 4/3·π·r³; (2) sphere packing density — SC, BCC, FCC, HCP, random close/loose packing fractions, ball count in a container and packed-bed bulk density. 100% in-browser.
Spherical Capacitor Calculator: Solid Sphere, Two Shells, Dielectric and More
Free spherical capacitor calculator: C = 4πε₀R for solid sphere, C =
Split Complementary Generator
Engineering-grade Split Complementary Color Scheme Generator, Color Wheel Harmonies Tool, and Photo Palette Extractor.
Spousal Support Calculator (SSAG) — Alimony Estimator + Buyout & Property Split
Free spousal support calculator: Canadian SSAG without-child and with-child (INDI) formulas, Rule of 65 duration, lump-sum alimony buyout present value, US state estimators (MA, TX, CT), Ontario property equalization and community-property split. 100% private, works offline.
Spring Rate Converter — N/mm, lb/in, kg/mm + Hooke, Series/Parallel & Wheel Rate Calculator
Free spring rate converter: convert N/mm, N/m, kN/m, lb/in, lb/ft, kg/mm, kgf/mm both ways. Includes Hooke's law F=k·x solver, series & parallel spring calculator, and wheel rate from motion ratio. 100% client-side.
Sql Converter
SQL String Escape — Online SQL Escape Tool
Free online SQL string escape tool: MySQL backslash mode, PostgreSQL/ANSI and SQL Server quote-doubling, per-character transformation table, worked examples. 100% client-side.
SQL FOR XML PATH Generator
Interactive T-SQL query generator for SQL Server string concatenation and XML data modeling using FOR XML PATH('').
SQL Generator
Interactive visual SQL query and DDL statement generator supporting MySQL, PostgreSQL, SQLite, and SQL Server.
SQL Linter - Free Online SQL Query Checker & Anti-Pattern Detector
Free online SQL linter: paste any query and get instant heuristic checks for SELECT *, missing WHERE on UPDATE/DELETE, implicit JOINs, trailing commas, keyword casing, N+1 patterns and more. 100% client-side.
Sql Query Formatter
SQL Query Sample Library & Builder
Interactive SQL query sample library and template builder covering Joins, CTEs, Window Functions, and Upserts across PostgreSQL, MySQL, SQL Server, and SQLite.
Sql To Csv
Extract data from SQL Insert statements into CSV.
Sql To Json
Convert SQL Insert statements to a JSON array.
SQL to MongoDB Converter
Free SQL to MongoDB converter: SELECT, WHERE, GROUP BY, INSERT, UPDATE, DELETE to Mongo shell, Mongoose and PyMongo. 100% client-side.
SQL Type Cast Generator
Interactive SQL CAST, CONVERT & TRY_CAST query builder across SQL Server, PostgreSQL, MySQL, Oracle, and SQLite.
SQL String Unescape — Online SQL Unescape Tool
Free online SQL string unescape tool: reverse MySQL backslash escapes, PostgreSQL '' doubling and E'' strings, SQL Server quote-doubling. Auto-detect dialect, double-escape warnings, round-trip verification. 100%% client-side.
Square Calculator — Square Footage & x² | nrtechstudio
Free square calculator: calculate square footage from length × width (ft, in, m), square any number x² with step-by-step work, multi-room totals, tile & flooring estimator with waste, and area unit conversions. 100% client-side.
Square Diagonal Calculator — Side ⇄ Diagonal + Area from Diagonal
Free square diagonal calculator: side to diagonal (d = s√2), diagonal to side (s = d/√2), area from diagonal (A = d²/2), live diagram, show-your-work steps and worked examples.
Square Feet Converter - Convert ft² to m², Acres, Hectares and More
Free square feet converter: convert ft² to square meters, acres, square yards, hectares, square miles and 4 more area units. Exact constants, worked examples, 2-way.
Square Feet to Cubic Feet Calculator - Area to Volume with Depth
Convert square feet to cubic feet: enter your area in square feet and a depth or thickness, and get the volume in cubic feet, cubic yards, cubic meters, and gallons. Includes a reverse depth finder and concrete/mulch presets.
Square Feet to Cubic Yards Calculator
Convert square feet to cubic yards: enter area and depth to get cubic yards, cubic feet, bag counts for mulch or soil, waste allowance, and a reverse depth mode. Free, no signup.
Square Inches Calculator — Area in in² (Rectangle, Circle, Triangle, Trapezoid)
Free square inches calculator: area in square inches for rectangle (L×W), circle (πr²), triangle (½bh), trapezoid ((a+b)/2×h), reverse side-from-area solver, and full conversion to sq ft, sq cm, sq yd, sq m, sq mm, acres.
Squat Max Calculator — Estimate Your 1RM (Epley, Brzycki, Lombardi)
Free squat max calculator: estimate your squat 1RM from weight × reps with Epley, Brzycki and Lombardi formulas. Training % table, rep-max chart, plate loader, bodyweight ratio, kg/lb.
SRI Hash Generator — Free Subresource Integrity Hash Generator (SHA-256/384/512)
Generate SRI integrity hashes online: SHA-256, SHA-384 and SHA-512 computed at once from text, files, or a URL. Snippet builder for <script> and <link> tags, verify mode, and a troubleshooting guide for failed integrity checks. Free, no signup, 100% client-side.
SSH Key Fingerprint Checker — MD5 & SHA256 Fingerprints + Randomart (Free)
Free SSH key fingerprint checker. Paste a public key to get MD5 & SHA256 fingerprints exactly like ssh-keygen -lf, visual randomart, and verify GitHub, GitLab & Bitbucket host keys. 100% client-side — keys never leave your browser.
SSH Keygen RSA & Key Pair Generator
Free online SSH keygen RSA and cryptographic key pair generator. Generate private keys, create public key from private key, and explore Ed25519 vs RSA.
SSL Certificate Decoder — Decode X.509, CSR & Check Private Key Match (Free)
Free SSL certificate decoder. Paste a PEM certificate to decode every X.509 field — subject, issuer, SAN, expiry, key usage, fingerprints. Also decodes CSRs and checks private-key match. 100% client-side — nothing is uploaded.
Staircase Calculator — Riser, Stringer, Code & Cost
Free staircase calculator: solve risers and treads, plan straight/L/U runs, lay out stringers, check IRC code, take off materials and estimate cost. 100% client-side.
Standard Error of the Mean Calculator (SEM) + Confidence Interval
Free standard error of the mean calculator: enter sample SD and n to get SEM = s/√n, plus a 90/95/99% confidence interval for the mean (z or t), t-critical table, and worked examples.
Standard Drink Calculator — Beer, Wine & Spirits (US NIAAA)
Free standard drink calculator: convert any beer, wine, or spirits serving to US standard drinks (14 g pure alcohol, NIAAA definition). Custom volume + ABV, session total, and beer/wine/shot equivalents. Educational tool.
Standard Equation of a Circle Calculator — (x-h)²+(y-k)²=r²
Free standard circle equation calculator: find (x-h)^2+(y-k)^2=r^2 from center+radius, three points, or general form x^2+y^2+Dx+Ey+F=0 (completing the square). Shows center, radius, general form and graph.
Standard Normal Curve Calculator & Z-Score Percentile Tool
Interactive standard normal curve calculator, standardized value z score, normal distribution curve z score, and percentile rank converter.
Standard Normal Distribution Calculator – Z Score & Probability
Standard normal distribution calculator, standard normal distribution probability calculator, z score meaning, z statistic formula, what does z score represent, define z score, normal distribution z score, how to get p value from z score, z to p value, calculator z test.
Startup Runway Calculator — How Long Will Your Cash Last? (Free, with Hiring & Revenue Scenarios)
Free startup runway calculator: enter cash, burn, hires and revenue growth to get your exact zero-cash date, fundraising deadline and best/base/worst scenarios. Month-by-month simulation, 100% private in your browser.
Startup Valuation Calculator — Pre/Post-Money, SAFE Note, Cap Table Dilution
Free startup valuation calculator: pre-money vs post-money valuation, SAFE note calculator (valuation cap, discount, MFN), multi-round cap table with dilution, and option pool shuffle. 100% private — runs in your browser.
Steak Cook Time Calculator | nrtechstudio.com
Steak cook time calculator: grill, pan-sear, broiler & reverse-sear times by thickness and doneness. Pull temps, rest times, USDA 145°F chart. Free tool.
Steps to Calories Calculator — Convert Steps to kcal (with Height)
Convert step count to calories burned. Enter steps + body weight (height optional) for a stride-based estimate, or reverse it: calories goal to steps needed. Free, no sign-up.
Stiffness Matrix Calculator | nrtechstudio
Free stiffness matrix calculator: axial bar (2x2), Euler-Bernoulli beam (4x4), 2D truss with angle transformation, and a 2-element assembly solver wit
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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.