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.
PECARN Calculator — Pediatric Head Injury CT Decision Rule (Kuppermann 2009) | nrtechstudio
Free PECARN pediatric head injury calculator (Kuppermann et al., Lancet 2009): age-specific predictors for children under 2 and ages 2–17, ciTBI risk
Pediatric Blood Pressure Percentile Calculator (AAP 2017) — nrtechstudio
Free pediatric blood pressure percentile calculator using the AAP 2017 normative tables (Flynn et al.). Enter age, sex, height, systolic & diastolic BP to get estimated BP percentiles and the AAP 2017 category: normal, elevated, stage 1 or stage 2. Educational use only.
Pediatric Epworth Sleepiness Scale (ESS-CHAD) Calculator — Child Daytime Sleepiness Test
Free ESS-CHAD calculator: the Epworth Sleepiness Scale for Children and Adolescents (Janssen et al.). Answer 8 questions, get the 0-24 score with norm
Pediatric GFR Calculator (Schwartz Formula) | nrtechstudio.com
Free pediatric eGFR calculator using the 2009 bedside Schwartz formula (eGFR = 0.413 x height / serum creatinine) for children, plus the original Schw
Pence to Pounds Converter & Calculator — Convert Pence to Pounds
Free pence to pounds converter and calculator. Convert pence to pounds (£ = p ÷ 100), pounds to pence, batch-convert lists, and look up old pre-decimal pence. How many pence in a pound? Exactly 100.
Peptide Reconstitution & Dosage Calculator — mg to mL to U-100/U-40 Syringe Units
Educational math only: convert peptide vial mg + water mL into concentration (mg/mL), draw volume (mL), and U-100 or U-40 insulin-syringe units; solve for diluent volume at a target concentration. Makes no dose recommendations.
Percentage Calculator — What Is X% of Y, X Is What % of Y, % Change — nrtechstudio
Free 3-in-1 percentage calculator: what is X% of Y, X is what percent of Y, and percent change old → new. Show-your-work steps, exact fractions, honest rounding notes. 100% client-side — your numbers never leave your browser.
Percent Change Calculator — Formula, Reverse Solver & Step-by-Step
Free percent change calculator with show-your-work steps: percent change between two numbers, reverse percent change solver, sequential percent changes, percent change vs percent difference and percentage points explained. 100% client-side, no signup.
Percent Difference Calculator — Symmetric % Difference Between Two Numbers (Free)
Free percent difference calculator (percentage difference): find the symmetric percent difference between two numbers with show-your-work steps, absolute difference, average, multi-pair mode, Excel formula, and worked examples. 100% client-side, no signup.
Percent Error Calculator — |E−T|/|T|×100 with Steps
Free percent error calculator: enter measured and theoretical values to get percent error, absolute error, signed error, step-by-step working, and accuracy interpretation.
Percent Increase Calculator
High-precision Percentage Increase Calculator, Percentage Change, Growth Rate & Step-by-Step Solver.
Percent Off Calculator — Sale Price, Stacked Discounts & Reverse Solver
Free percent off calculator: sale price, discount amount, stacked discounts (20% off + extra 10%), tax-inclusive totals, reverse original-price solver, and deal comparison. 100% private, runs in your browser.
Percent Solution Calculator — % w/w, % w/v, % v/v + ppm Converter
Free percent solution calculator: prepare % w/w, % w/v and % v/v solutions, solve for solute mass, solvent volume or final concentration, and convert % ↔ ppm ↔ ppb with worked lab examples.
Percent to Ratio Calculator: Convert % to Ratio, Ratio to % and Slope Grade
Free percent to ratio calculator with exact integer math. Convert percent to ratio (25% to 1:3), ratio to percent (1:3 to 25%), and slope percent to ratio grade (10% to 1:10). Includes common percent table 1 to 99 and worked examples.
Percent to Total Calculator: Find the Total, Part, or Percent - nrtechstudio
Free percent to total calculator: X is P% of the total, find the total (e.g. 45 is 30% -> 150). Also solves P% of total and X of total as percent. Exact fractions, show-your-work steps, 100% client-side.
Percent Tolerance Calculator — Min/Max Range & Reverse | nrtechstudio
Free percent tolerance calculator: enter a nominal value and ± tolerance to get the min/max range, boundary table and band visualization. Reverse mode finds nominal ±% from min/max. For resistors, mac
Percentage Decrease Calculator — Formula, Reverse Solver & Step-by-Step
Free percentage decrease calculator with show-your-work steps: percent decrease between two numbers, reverse solvers (find the new or original value), sequential discounts (30% then 20% ≠ 50%), sale discount, weight loss and price drop examples. 100% client-side, no signup.
Percentile Calculator: P-Value, Percentile Rank, Quartiles & Box Plot | NRTechStudio
Free percentile calculator: paste any dataset to get the value at any percentile (P50, P90, ...), percentile rank of a score, Q1/Q3/IQR, and a box plot — with linear interpolation or nearest-rank method.
Pergola Size Calculator — Posts, Beams, Rafters, Shade %, Materials & Cost
Pergola size calculator: size by function and guests, post/beam spacing, rafter shade %, material takeoff, cost for lumber/cedar/aluminum + standard s
Period Calculator — Next Period Predictor & Cycle Tracker | nrtechstudio.com
Free period calculator: predict your next 6 periods from your last period date and cycle length, analyze cycle regularity from your history, see PMS windows on a 3-month calendar. 100% client-side, no signup, no app needed.
Period to Frequency Calculator | T = 1/f, Angular Frequency and Wavelength
Free two-way period to frequency calculator: f = 1/T and T = 1/f with s, ms, us, ns and Hz, kHz, MHz, GHz units, plus angular frequency (omega = 2 pi f) and vacuum wavelength (lambda = c/f). 100% client-side.
Pest Control Cost Lab — How Much Does Pest Control Cost? Termite, Bed Bug & Exterminator Price Calculator
Free pest control cost lab: per-pest price estimates for termites, bed bugs, cockroaches, rodents, wasps & fleas; termite treatment method comparator (fumigation vs bait vs liquid barrier vs heat); per-linear-foot termite engine; quarterly-plan vs one-time total cost; DIY-vs-pro gate; 50-state pricing multipliers. 100% client-side.
Pet Food Calculator — How Much to Feed Your Dog Cat (Vet RER/MER Formula)
Free pet food calculator: find exactly how much to feed your dog or cat per day in grams and cups. Vet-grade RER/MER calorie formula, puppy, senior, weight-loss plans, wet & dry mix, multi-pet mode. 100% client-side, no signup.
Pet Sitter Rates Calculator — Fair Prices for Sitting, Boarding & Dog Walking
Free pet sitter rates calculator: estimate fair drop-in visit, dog walking, boarding & overnight sitting prices by pets, location & holidays. Sitter pricing advisor + quote checker included.
P/E2 Ratio Calculator — Progesterone to Estradiol Ratio + Unit Converter
Calculate your progesterone-to-estradiol (P/E2) ratio with automatic unit conversion (ng/mL ↔ nmol/L, pg/mL ↔ pmol/L). IVF trigger-day and mid-luteal
PHEV Economy Calculator — Blended MPGe, Cost per Mile & Payback
Free plug-in hybrid economy calculator: blended MPGe from your electric miles (kWh) and gasoline gallons, monthly energy cost, cost per mile split, savings vs a gas-only car, and payback on the PHEV p
Phone Number Formatter Online
Free online phone number formatter, telephone number formatting tool, and proper phone number format generator. Format mobile phone number format, E.164, and JS code.
Photo Size Lab — Megapixel, Print Size Image File Size Calculator
Free photo size calculator: megapixel to print size, pixels needed for any print size at 300/150 DPI, JPEG/RAW/HEIC/PNG file size estimator, memory card storage planner, and social media image size specs. 100% in your browser.
PHP Linter Online — Check PHP Syntax & Code Issues
Free online PHP linter. Heuristic client-side checks for missing semicolons, unbalanced brackets, short open tags, deprecated mysql_* calls, eval() risks and style issues. No uploads, no signup.
Physical Pendulum Calculator — Period, Equivalent Length & COM Solver
Free physical pendulum calculator: T = 2π√(I/m·g·d) from I, m, d, g; 5 rigid-body presets (rod, disk, sphere, hoop) with parallel-axis inertia; equiva
Pi Attenuator Calculator — Pi & T RF Attenuator Resistor Values
Design Pi and T resistive attenuators: enter attenuation in dB and impedance in ohms to get exact resistor values, nearest E12/E24 standard values, and actual built attenuation.
Pickleball Court Lab — Dimensions, Layout Planner & Tennis Conversion
Interactive pickleball court dimension explorer, space-fit planner, tennis-court conversion layouts, paint guide and net setup — all specs per USA Pickleball official rules.
Picture Frame Size Calculator — Mat, Glass & Gallery Wall Planner
Free picture frame size calculator: frame size from artwork and mat width, mat opening calculator, standard frame sizes chart, glass size, and gallery wall spacing planner.
Pine Straw Calculator — How Many Bales Do I Need?
Free pine straw calculator: how many bales you need for your beds, bale to square-foot coverage converter, pine straw vs mulch cost per sq ft, and annual re-mulch top-up. Coverage rates verified from
Pinewood Derby Speed Lab — CoG Solver, Weight Planner, Rail-Riding & Rules Checker
Free pinewood derby speed lab: center-of-gravity solver, 5 oz weight budget planner, rail-riding setup calculator, wheel/axle prep checklist, graphite vs Krytox lube advisor, and BSA rules checker. 100% client-side, no signup.
Pint to Pound Converter: Volume to Weight via Density
Convert pints to pounds and pounds to pints using density. Supports US liquid pint, US dry pint, and imperial pint with presets for water, milk, oil, honey, flour, and sugar.
Pipe Flow Calculator — Flow Rate from Head Loss (Darcy–Weisbach + Colebrook–White)
Free pipe flow calculator: solve flow rate Q and velocity from head loss or pressure drop in a full pressurized pipe using Darcy–Weisbach with the iterative Colebrook–White friction factor. Reports Reynolds number, flow regime and friction factor; reverse-solves pipe diameter from a target flow rate
Pipe Velocity Calculator — Flow Rate ↔ Velocity, Velocity Head & Reynolds
Free pipe velocity calculator: convert flow rate to velocity (v=Q/A) with GPM, m³/s, ft³/s ↔ m/s, ft/s units, velocity head v²/2g, Reynolds number, API 14E erosional velocity, water-hammer guideline and a Schedule-40 pipe ID table. 100% in-browser.
Pipe Volume Calculator
Pipe volume calculator: internal capacity from ID x length in gallons, litres and ft3, partial fill, multi-section system volume, reverse length and NPS schedule table.
Piston Force Calculator — Hydraulic & Pneumatic Cylinder Force, Bore Sizer
Free piston force calculator: hydraulic cylinder force from pressure and bore, pneumatic extend and retract force with rod annulus, inverse bore sizin
Piston Speed Calculator — Mean & Max Piston Speed, RPM Limit Solver
Free piston speed calculator: mean piston speed from stroke and RPM, peak instantaneous speed, safe-limit verdict, and a reverse solver for maximum RPM.
Pixels Inches Conversion – DPI, PPI & Print Resolution
Pixels inches conversion, translate pixels into inches, px inches conversion, converter px, in to px conversion, dpi to px conversion.
Pizza Comparison Calculator — Compare Pizza Value by Size | nrtechstudio.com
Compare up to 3 pizzas by diameter and price: area in square inches, price per sq inch, price per slice, value ranking and % savings. Free, instant, no sign-up.
Plant Population Calculator — Plants per Acre, Hectare & Seeding Rate | nrtechstudio.com
Free plant population calculator: plants per acre & hectare from row and in-row spacing, reverse spacing finder, seeding rate, seed-bag & field planner. Corn, soybean, wheat, cotton reference tables. 100% private — runs in your browser.
Planter Box Size Calculator — 7 Ways to Size & Build a Planter Box
Free online planter box size calculator with 7 modes: size planter boxes by plant type, compute soil volume in cubic feet, gallons and bags, plan drainage holes, generate a cedar lumber and materials list, check elevated-planter leg height and loaded weight, lay out multiple boxes on a patio, and estimate build cost. Runs 100% in the browser.
Planting Calendar 2026–2027: When to Plant Vegetables by Zone State (Free)
Free garden planting calendar by USDA zone, US state, and 30+ international regions. 67 vegetables, herbs & flowers with indoor-sow, transplant & direct-sow dates, frost dates, a what-to-plant-now planner, and print-friendly monthly view. 100% client-side — your data never leaves your browser.
Plasma Osmolality Calculator — Calculated Posm & Osmolar Gap
Free plasma osmolality calculator: calculated Posm = 2×Na + glucose/18 + BUN/2.8 (+ ethanol/4.6), osmolar gap = measured − calculated, mg/dL ↔ mmol/L
Plasma Volume Calculator (Kaplan, Hakim) | nrtechstudio.com
Free plasma volume calculator: estimate plasma volume from total blood volume and hematocrit, or directly with the Kaplan and Hakim formulas. Ideal pl
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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.