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.
Rabbit Gestation Calculator — Due Date, Nest Box Timing & Kindling Checklist
Free rabbit gestation calculator: enter the breeding date to get the kindling due-date window (28–35 days), nest box timing, pregnancy timeline, litter guide, and false-pregnancy check.
Radar Horizon Calculator — Radar Horizon Distance, Line of Sight & Fresnel Zone
Calculate radar horizon from antenna height (4/3 refraction model), radar range to elevated targets, and check line of sight + Fresnel zone clearance. Results in km, miles, and nautical miles. Free, 100% client-side.
Radiation Pressure Calculator — Sunlight, Solar Sails & Photon Pressure | nrtechstudio
Free radiation pressure calculator: P = (1+R)·I·cos²θ/c from irradiance, from source power & distance (Sun presets), solar-sail thrust F = P·A with Δv
Rust Raid Calculator — Satchels, C4, Rockets & Sulfur Cost (Rust Game)
Rust game raid cost calculator: how many satchel charges, C4, rockets or explosive 5.56 ammo you need per wall and door tier, with total sulfur, charcoal and time. Verified Oct 2026.
Model Railroad Grade Calculator: Helix, Incline & Grade Solver | Railroad Grade Lab
Free model railroad grade lab: grade percent/ratio/angle solver, helix designer, curve grade compensation, riser height planner, max-grade advisor by scale, and Woodland Scenics incline set matcher. 100% client-side, no signup.
Rain Barrel Size Calculator — Roof, Harvest, Diverter & Payback
Free rain barrel size calculator: size barrels from roof area and rainfall, plan monthly harvest, barrels needed, first-flush diverter, gutter and downspout check, garden usage and payback. 100% client-side.
Rain to Snow Conversion Calculator — 10:1 & Temperature-Adjusted Ratios
Free rain to snow conversion calculator: convert rain (inches/mm) to snowfall (inches/cm) with the classic 10:1 rule or a temperature-adjusted ratio, plus reverse snow-to-rain, ratio table, worked examples and FAQ.
Raise Lab — Pay Raise Calculator: Raise % to New Pay, Reverse, Multi-Year, After-Tax, Real vs Nominal (Free)
Free pay raise calculator suite: raise % to new pay (hourly/weekly/biweekly/monthly/annual), reverse raise %, multi-year compounding projection, after-tax net raise, real vs nominal raise with inflation, pro-rata & retroactive pay, and India salary-hike CTC to in-hand. 100% client-side, no signup.
Raised Bed Size Calculator — 7 Ways to Size Your Garden Bed
Free raised bed size calculator with 7 modes: size beds by crop and reach rule, soil volume in cubic feet and bags, wheelchair sizing, UK metric, layo
RAM True Latency Calculator (DDR3/DDR4/DDR5) — CL to Nanoseconds
Convert CAS latency (CL) to true latency in nanoseconds for DDR3, DDR4 and DDR5. Compare two RAM kits, estimate bandwidth, and see why DDR5 CL30 equals DDR4 CL16.
Random Animal Generator
Generate random animals, mythical beasts, and creature names.
Random Color Wheel & Spinning Name Picker
Free interactive random color wheel, random color selection generator, and spinning wheel name generator for giveaways, raffles, and design palettes.
Random Football Name Generator, Wheel Picker & Random Order Generator
Free online random football name generator and wheel random name generator. Generate random name generator for teams, shuffle random order generator lists, and run fair name generator competition draws.
Random HSL Gen
Random HSL color generator with hue-arc ranges, per-channel H/S/L locks, batch generation, harmony palettes, and one-click HEX/RGB/HSL copy — 100% client-side.
Random IP Generator — Random IPv4 & IPv6 Address Generator
Free random IP generator: bulk random IPv4 and IPv6 addresses, custom subnet/CIDR ranges, public/private filters, copy and download. 100% client-side.
Random IPv6 Gen — Random IPv6 Address Generator
Free random IPv6 address generator: global unicast, ULA, link-local and documentation prefixes, full + RFC 5952 formats, EUI-64 from MAC, bulk up to 100.
Random Letter of the Alphabet Generator – 3 & 4 Letter Studio
Random alphabet generator, random letter of the alphabet generator, random 4 letter generator, random 3 letter generator.
Lettering Text Generator & Random Number Generator 1-150
Free online lettering text generator, script text generator, and random number generator 1-150. Convert text into cool Unicode fonts, cursive script, block text, and pick random numbers.
Random Number Generator 1-50 & Lottery Suite
Precision random number generator 1-50, 1-100, lottery number generators, 3/4/6 digit code generator, and without replacement randomizer list.
Random Number Generator
Engineering-grade, cryptographic Random Number Generator, sequence chooser, digit code generator, and list selector.
Random Port Generator — Free TCP/UDP Port Number Generator
Generate cryptographically secure random port numbers with custom ranges, bulk mode, browser-blocked port avoidance and a common-ports reference table. 100% client-side.
Random RGB Gen
Engineering-grade Random RGB Color Generator, Color Palette Randomizer, Hex Code Chooser, and Scheme Creator.
Random Sample Data Generator
Random number generator with animation, number randomiser 1-10, number ordering generator, number generator without repeats, 5 number generator, random number picker.
Random Skin Color & Random Letter Generator
Dual creative studio: Random skin color generator with realistic Fitzpatrick undertones and fantasy hues, plus random letter generator and alphabet randomiser.
Range Hood CFM Calculator — What Size Hood Do I Need? | nrtechstudio.com
Size a kitchen range hood in CFM with 7 methods: gas BTU rule, HVI width tables, room volume, duct loss, makeup-air check, sones and hood-width picker
Rat Cage Size Calculator — How Big Should a Rat Cage Be?
Free rat cage size calculator: floor area and cage volume per rat (2.0 cu ft minimum, 2.5 cu ft comfort standard), bar spacing safety check, bedding estimator, and suggested cage dimensions for 1–8 ra
Ratio Simplifier Calculator: Simplify a:b and a:b:c to Lowest Terms
Free ratio simplifier calculator for 2 or 3 numbers. Reduce any ratio to simplest form (8:12 to 2:3, 6:9:12 to 2:3:4) with GCD steps, decimal forms and equivalent ratios. Exact math, no rounding errors.
Rational or Irrational Calculator — Classify Any Number | nrtechstudio.com
Free rational or irrational numbers calculator: enter a decimal, fraction, or constant like √2, π, or e and get the classification with the exact p/q form, decimal expansion, and a proof sketch.
Rational Zeros Calculator — Rational Root Theorem Finder | nrtechstudio
Free rational zeros calculator: enter polynomial coefficients, get all possible rational roots (±p/q), synthetic division test results, actual rational zeros, and partial factorization.
Raw Dog Food Calculator — Daily BARF & Prey Model Portions by Weight
Free raw dog food calculator: daily portions as % of body weight, BARF (70/10/10/5/5) and prey model (80/10/10) component grams, transition guide, and raw feeding cost. 100% client-side, no signup.
Raw Score to Scaled Score Converter: LSAT and STAAR
Convert a raw score (number correct) to a scaled score. LSAT 120-180 estimator, official STAAR raw-to-scale lookup tables (TEA 2025), and a generic raw-to-scale mapper.
RC Circuit Calculator — Time Constant, Charging & Discharging Curves, 555 Timer
Free RC circuit calculator: time constant tau = R·C, charging Vc(t) = V(1−e^(−t/τ)) and discharging curves with SVG plots, time-to-percentage solvers,
RCRI Calculator — Revised Cardiac Risk Index for Surgery (Educational) — NR Tech Studio
Free RCRI calculator: estimate perioperative cardiac risk for noncardiac surgery from the 6 Revised Cardiac Risk Index predictors (Lee 1999), with risk classes I–IV, derivation and validation cohort rates, contemporary re-estimates, and ACC/AHA guideline context. Educational tool — not medical advic
Flesch Reading Ease & Automated Readability Index Calculator
Interactive readability score calculator measuring Flesch Reading Ease, Automated Readability Index (ARI), and grade level metrics.
Readability Score Calculator
Standalone professional Flesch-Kincaid readability calculator and text readability analyzer. Compute Flesch Reading Ease, Flesch-Kincaid Grade Level, Gunning Fog, Coleman-Liau, and ARI.
Reading Level Converter — Lexile, FP, DRA, ATOS, PM Grade Level
Free reading level converter for teachers: convert between Lexile, Fountas & Pinnell guided reading levels, DRA, ATOS, PM Benchmarks and grade level. Plus a text analyzer (Flesch-Kincaid, Fry graph, SMOG, Dale-Chall, Gunning Fog, Coleman-Liau) and a Fry book-leveling tool. 100% client-side — your text never leaves your browser.
Real Estate Commission Calculator — Splits & Net Proceeds
Free real estate commission calculator: total commission,
Rebar Calculator — Quantity, Weight, Spacing & Cost Estimator
Estimate rebar for slabs, footings, columns and beams: bar counts, total linear feet, weight per foot (ASTM A615 table), lap splice length and cost. 100% client-side.
Recessed Lighting Calculator — Layout, Spacing & Fixture Count
Free recessed lighting layout calculator: how many can lights you need, spacing between fixtures, distance from walls, and a scaled grid diagram. Based on the lumen method and the half-ceiling-height spacing rule.
Recipe Cost Calculator — Ingredient Cost, Per Serving & Food Cost % | nrtechstudio.com
Free recipe cost calculator: price every ingredient from its package size, get total recipe cost, cost per serving and per unit, food cost %, and a suggested selling price with your target margin. Includes a recipe scaler and kitchen unit converter. 100% client-side, no signup.
Recipe Nutrition Calculator — Calories & Macros Per Serving
Free recipe nutrition calculator: enter ingredients to get per-serving calories, protein, carbs, fat, fiber, sugar, sodium, macro split & % Daily Values. 228-ingredient USDA-based database. 100% private, no signup.
Recipe Scaler — Scale Recipes Up Down + Cups to Grams Converter
Free recipe scaler: halve, double, or triple any recipe with smart scaling. 100+ ingredient density database converts cups to grams per ingredient, with non-linear leavening rules, pan size converter & convection temp adjustment. 100% client-side, no signup.
Free Recoil Energy Calculator — Firearm Recoil in ft·lbf & Joules
Calculate free recoil energy, recoil velocity, and recoil impulse for any firearm load. Bullet weight in grains, velocity in fps, powder charge with h
Rectangular Pyramid Volume Calculator — Volume, Slant Height & Surface Area
Free rectangular pyramid volume calculator: enter base length, width and height to get volume (V=lwh/3), both slant heights, lateral and total surface area, with diagram and step-by-step working.
UK Statutory Redundancy Pay Calculator (2026 Rates)
UK statutory redundancy pay calculator: estimate your 2026 entitlement with age-banded weeks and the capped weekly rate (£751 GB / £783 NI).
Reef Dosing Calculator — Ca/Alk/Mg, Kalkwasser & Vodka Dosing
Free reef tank dosing calculator: calcium, alkalinity & magnesium dosing, kalkwasser/limewater dosing, vodka/vinegar carbon dosing ramp, KNO3 nitrate dosing, daily-dose planner and product database. 100% client-side.
Refrigerant Capillary Tube Calculator — Sizing Estimator (R134a, R600a, R290, R404A, R32)
Free refrigerant capillary tube sizing calculator for R134a, R600a, R290, R404A and R32. Estimate capillary length from cooling capacity, condensing and evaporating temperatures, and bore size using a documented homogeneous-equilibrium flow model — every assumption exposed.
Refrigerant Line Set Charge Calculator (oz/ft) — HVAC Tech Tool
Calculate the additional refrigerant charge for a line set: enter liquid line diameter, total lineset length, and factory charge length to get the add/remove adjustment in oz, lb, and grams. For certified HVAC technicians (EPA 608).
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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.