Tools in This Collection
Battery Size Chart
Battery types, dimensions, voltage, and common applications
Paper Sizes Reference
US Letter, A4, and all standard paper dimensions in mm and inches
Time Zone Reference
UTC offsets, DST rules, and current local times by region
Country Calling Codes
International dialing prefixes for all countries
Holiday Shipping Deadlines
Carrier cutoff dates for major US holidays
Meteor Shower Calendar
Annual meteor shower peak dates, rates, and radiant constellations
How to Read a Pay Stub
Decode gross pay, deductions, FICA, and net pay on your paycheck
How to Read a Ruler
Imperial and metric ruler markings and fraction guide
How to Read a Tape Measure
Tape measure markings including stud spacing and framing marks
How to Read a Tire Sidewall
Decode tire size, load index, speed rating, and DOT date code
HTML Entities Reference
Named HTML entities and numeric character codes
HTTP Headers Reference
Common HTTP request and response headers with examples
HTTP Request Methods Reference
GET, POST, PUT, DELETE and all HTTP methods with idempotency rules
General and Tech Reference Lookups
General reference needs span from everyday practical questions (what's the difference between AA and AAA batteries?) to technical developer references (which HTTP methods are idempotent?). These tools are designed for fast, precise answers — no scrolling through Wikipedia or reading through specifications documents.
Battery Sizes: Types, Dimensions, and Applications
Standard alkaline battery sizes: AAA (1.5V, 1000-1200 mAh, 10.5mm dia × 44.5mm long) for remote controls and small devices; AA (1.5V, 2500-3000 mAh, 14.5mm dia × 50.5mm long) for cameras, toys, flashlights; C (1.5V, 8000 mAh, 26.2mm dia × 50mm) for flashlights and toys; D (1.5V, 12000-18000 mAh, 34.2mm dia × 61.5mm) for high-drain devices and lanterns; 9V (9V, 500-600 mAh) for smoke detectors and multimeters. Button cells: CR2032 (3V lithium, 20mm dia × 3.2mm) for watches, key fobs, calculators; LR44 (1.5V alkaline, 11.6mm dia) for small electronics. The Battery Size Chart covers all standard types including rechargeable NiMH and lithium variants.
Paper Sizes: US vs International
US Letter (8.5" × 11" / 215.9mm × 279.4mm) is the standard US document size. Legal (8.5" × 14") is used for contracts. Tabloid/Ledger (11" × 17") for spreadsheets and posters. International A-series: A4 (210mm × 297mm / 8.27" × 11.69") is the world standard for documents. A3 (297mm × 420mm) is A4 doubled. A5 (148mm × 210mm) is A4 halved — used for flyers. B-series: B4 (250mm × 353mm) common for envelopes and books in Asia. Key difference: US Letter is slightly wider than A4 but shorter; documents formatted for one don't print perfectly on the other. The Paper Sizes Reference covers all A, B, C (envelope), and US standard sizes in both mm and inches.
How to Read a Tire Sidewall
A tire marked P225/65R17 encodes five values: P = passenger car (LT = light truck); 225 = tire width in millimeters; 65 = aspect ratio (sidewall height as % of width = 225 × 0.65 = 146mm sidewall); R = radial construction; 17 = rim diameter in inches. Load index and speed rating follow: 95H means 1,521 lbs load capacity at up to 130 mph. DOT manufacturing date: the last 4 digits of the DOT code give week and year (2023 = week 20 of 2023). The How to Read a Tire Sidewall guide decodes all markings including UTQG treadwear, traction, and temperature grades.
Time Zones, Calling Codes, and Calendar References
The Time Zone Reference lists all UTC offsets with country and region examples, including which zones observe DST and when. The Country Calling Codes reference covers international dialing prefixes for all 195 countries. The Meteor Shower Calendar lists peak dates, radiant constellations, and expected rates for major annual meteor showers. The Holiday Shipping Deadlines reference shows carrier cutoff dates for major US holidays.
Reading Tools and Measurement Guides
The How to Read a Pay Stub guide decodes gross pay, federal and state withholding, FICA (6.2% Social Security + 1.45% Medicare), pre-tax deductions (401k, health insurance), and net pay. The How to Read a Ruler and How to Read a Tape Measure guides cover the 1/16" fractions on standard imperial rulers and the special markings on framing tapes (red marks every 16" for stud spacing).
Developer Quick References
The HTML Entities Reference covers all named entities (&, <, >, ©, ®, etc.) and common Unicode characters with their numeric codes. The HTTP Headers Reference lists common request and response headers with their purpose and example values. The HTTP Request Methods Reference explains GET, POST, PUT, PATCH, DELETE, HEAD, OPTIONS, and CONNECT with idempotency, safety, and typical use cases — essential for API design and debugging.
Frequently Asked Questions
What is the difference between AA and AAA batteries?
AA batteries are larger (14.5mm diameter × 50.5mm long) with higher capacity (2,500-3,000 mAh) and longer life. AAA batteries are smaller (10.5mm diameter × 44.5mm long) with lower capacity (1,000-1,200 mAh). Both are 1.5V alkaline. AA is used in cameras, toys, and remotes requiring more power; AAA is used in smaller devices like TV remotes, headphones, and small flashlights. They are not interchangeable — device battery compartments are sized for one or the other.
What is the difference between US Letter and A4 paper?
US Letter is 8.5" × 11" (215.9mm × 279.4mm). A4 is 210mm × 297mm (8.27" × 11.69"). Letter is slightly wider (8.5" vs 8.27") but shorter (11" vs 11.69"). Documents formatted for A4 will have content cut off when printed on Letter, and vice versa. For international documents, use A4 formatting. The practical difference matters most for margins — A4 documents often need margin adjustments when printed on Letter paper.
How do I decode a tire size like P225/65R17?
P225/65R17 breaks down as: P = passenger car tire; 225 = section width in millimeters; 65 = aspect ratio (sidewall height is 65% of 225mm = 146mm); R = radial construction; 17 = rim diameter in inches. A tire marked P235/60R17 is wider (235mm), lower profile (60%), same rim size (17"). Higher aspect ratio = taller sidewall = more flex. Lower profile = stiffer, sportier feel, typically on wider tires.
Which HTTP methods are idempotent?
Idempotent methods produce the same result when called multiple times with the same input: GET, HEAD, PUT, DELETE, OPTIONS. Non-idempotent: POST (creates new resources each call) and PATCH (depends on implementation). Safe methods (read-only, no side effects): GET, HEAD, OPTIONS. Understanding idempotency matters for API design and error recovery — you can safely retry an idempotent request if you're unsure the first attempt succeeded.