Everyday questions.
Clear calculations.

Convert real-world measurements to model dimensions and model dimensions back to real size using a 1:X scale ratio and clearly labeled length units, with named presets for architectural drawing scales and model railroad scales.

Calculate display pixels per inch from pixel width, pixel height, and diagonal size, with aspect ratio, pixel diagonal, and screen area context.

Use the named oc-bra-legacy-v1 two-measurement method as a non-universal try-on estimate, then verify fit with the intended manufacturer.

Perform fixed 2 by 2 matrix addition, subtraction, multiplication, determinant, and transpose with formulas, examples, and singular-matrix notes.

Calculate percent of a number, what percent one value is of another, and percent change with clear formulas, examples, domains, and interpretation.

Compare facial measurements against golden-ratio and facial-thirds proportions as an aesthetic novelty — a playful analysis, not a scientific beauty test.

Generate pseudo-random integers or decimals within a chosen range, with optional no-duplicate draws for everyday sampling, games, and classroom examples.

Calculate gratuity, total bill, and per-person split from a bill amount, tip percentage, and party size for restaurants, delivery, salons, rides, and other service bills.

Calculate molarity from moles of solute and liters of solution, with amount concentration definition, units, lab cautions, and checked examples.

Calculate concrete volume for slabs, columns, tubes, curbs, and stairs, with package count and dry-mix weight from entered bag yield and weight assumptions.

Calculate the slope between two points, identify rise and run, interpret positive, negative, zero, and undefined slopes, and connect slope to linear rates of change.

Convert between sone, phon, and dB sound levels with the calculator's 1 kHz assumption: dB equals phon at 1 kHz, and sone uses a logarithmic loudness formula.

Compare counted round, square and rectangular pan bases in inches or centimeters. Find the area multiplier for the same positive intended depth.

Added Oct 4, 2026

Convert frequency to the duration of one cycle, or period to frequency. Supports Hz, kHz, MHz, GHz, seconds, milliseconds, and microseconds.

Added Oct 4, 2026

Estimate laundry loads from measured dry laundry weight and your chosen usable weight per load. See the minimum load count and an evenly divided load weight.

Added Oct 4, 2026

Scale an ingredient list from the original serving count to your desired servings. Keep each ingredient’s unit, show fractional quantities, and copy the resized list.

Added Oct 4, 2026

Calculate wavelength, frequency, or wave speed using v = fλ. Choose exact light speed in vacuum or enter a speed, with SI prefixes and scientific notation.

Added Oct 4, 2026

Check a loaded school backpack against a child's body weight using the AAP 15% guidance, with a category label and a recommended pack-weight range in kg or lb.

Added Aug 10, 2026

Calculate audiobook listening time, time saved, and planned break time from original duration, playback speed, and break schedule.

Updated Oct 4, 2026

Find the average of two to five percentages, with the simple mean formula, equal-weight guidance, and when weighted totals are the honest answer.

Updated Oct 4, 2026

Convert statute miles to kilometers using the exact international relationship 1 mi = 1.609344 km.

Updated Oct 4, 2026

Calculate percent increase or decrease from an original value to a new value, with absolute change and clear guidance on baseline, sign, and zero-value limits.

Updated Oct 4, 2026

Convert real-world measurements to model dimensions and model dimensions back to real size using a 1:X scale ratio and clearly labeled length units, with named presets for architectural drawing scales and model railroad scales.

Updated Oct 4, 2026

Add a per-student school supplies list with quantities and unit prices, then see the total cost, remaining budget, and any overage.

Updated Oct 4, 2026

Calculate audiobook listening time, time saved, and planned break time from original duration, playback speed, and break schedule.

Verified Oct 4, 2026

Find the average of two to five percentages, with the simple mean formula, equal-weight guidance, and when weighted totals are the honest answer.

Verified Oct 4, 2026

Compare counted round, square and rectangular pan bases in inches or centimeters. Find the area multiplier for the same positive intended depth.

Verified Oct 4, 2026

Convert frequency to the duration of one cycle, or period to frequency. Supports Hz, kHz, MHz, GHz, seconds, milliseconds, and microseconds.

Verified Oct 4, 2026

Estimate laundry loads from measured dry laundry weight and your chosen usable weight per load. See the minimum load count and an evenly divided load weight.

Verified Oct 4, 2026

Convert statute miles to kilometers using the exact international relationship 1 mi = 1.609344 km.

Verified Oct 4, 2026