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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.

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

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

Count business days between two dates, excluding weekends and any holidays you add, with calendar days, weekends, and full weeks.

Added Aug 10, 2026

Estimate a daily water target from the NASEM adequate intake for total water scaled to your weight, plus an exercise add-on, with liters, milliliters, and cups.

Added Aug 10, 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

This scientific notation converter and calculator converts decimal numbers to scientific notation or expands scientific notation back to standard form, with E notation, exponent rules, examples, and edge-case guidance.

Updated Oct 4, 2026

Estimate the army body fat percentage with the AR 600-9 circumference method from height, neck, waist, and (for women) hip measurements, with the age-band screening-table maxima shown for reference only.

Updated Aug 18, 2026

Calculate an ideal no-air-resistance projectile scenario from user-entered speed, angle, and release height. Results are not actual or official shot-put distances.

Updated Aug 14, 2026

Explore an unvalidated activity, diet, and smoking worksheet for eye-health education. It does not test 20/20 vision or estimate your risk of eye disease.

Updated Aug 14, 2026

Find the calendar or weekday-only end date for a 30 day challenge, trial, return window, reminder, savings sprint, or habit plan.

Updated Aug 14, 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

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.

Verified 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.

Verified Oct 4, 2026

This scientific notation converter and calculator converts decimal numbers to scientific notation or expands scientific notation back to standard form, with E notation, exponent rules, examples, and edge-case guidance.

Verified Oct 4, 2026

Estimate the army body fat percentage with the AR 600-9 circumference method from height, neck, waist, and (for women) hip measurements, with the age-band screening-table maxima shown for reference only.

Verified Aug 18, 2026