The right number.Right away.
Scientific calculators and converters. Every tool states its formula, its limits of validity and its primary source.
CommonGCD and LCMHooke’s law4-20 mA scalingBattery runtimeForce converterDNA sequence analyzer
- 103
- published tools
- 11
- fields
- 100%
- free, no account
- 126
- documented decisions
Today’s trap
A 100% slope is not a wall.
It is 45°, the angle where you climb as much as you advance. The percentage is a tangent: it grows without bound, and vertical has none.
Check it in the tool · Slope: percent, degrees, ratio →Out at 60 km/h, back at 40: the average is not 50.
It is 48 km/h. The slow leg takes more time than the fast one, and the average leans towards it: total distance over total time, always.
Check it in the tool · Speed, distance, time →The iceberg 89% underwater is not an image.
It is a quotient: 917 kg/m³ of ice over 1025 of sea water. A floating body sinks until it displaces exactly its own weight.
Check it in the tool · Archimedes’ buoyancy →Your "20,000 mAh" power bank never serves 20,000.
Those mAh are counted at 3.7 V: 74 Wh. Recounted at USB’s 5 V, 14,800 remain, minus losses. The maker did not lie, it chose its unit.
Check it in the tool · Battery runtime →Carrying a suitcase provides no mechanical work.
The force is vertical, the displacement horizontal: cos 90° = 0. The fatigue is real, but muscular: the physicist and the porter count different things.
Check it in the tool · Work and power →The most abundant reactant can be the one that runs out.
Moles divided by coefficients decide, not masses nor moles alone. Comparing grams is the mistake marked in red on exam papers.
Check it in the tool · Stoichiometry and limiting reactant →With matrices, A×B and B×A are two different answers.
Matrix multiplication is not commutative: the order carries information. The tool always computes both, because comparing beats warning.
Check it in the tool · 2×2 and 3×3 matrices: determinant, inverse, system →Stretching a spring twice as far stores four times as much.
The energy is ½kx², the area of the triangle under the force-extension line. That is why a bow is drawn full length: the last centimetres pay the most.
Check it in the tool · Hooke’s law →A one-centimetre tube presses as much as a lake.
Ten metres below the surface, the pressure is the same in both: it depends only on the water height, never the volume. That is the hydrostatic paradox.
Check it in the tool · Hydrostatic pressure →A 5 W standby beats your washing machine over the year.
5 W around the clock make 43.8 kWh a year: standby is about the 8760 hours, not the power. The most profitable calculation in the house.
Check it in the tool · Electricity consumption →A podium of 3 makes six times more cases than a committee of 3.
One question separates the two counts: does order matter? Gold-silver-bronze is a permutation, a trio is a combination, and 3! = 6 stands between them.
Check it in the tool · Combinations, permutations and factorial →Under water, red stays red.
Changing medium, a wave keeps its frequency: the wavelength adapts to the speed, a quarter shorter in water. Colour follows the frequency.
Check it in the tool · Waves: frequency and wavelength →"250" does not say how many significant figures it has.
Two or three? Trailing zeros of an integer are ambiguous: "250." or "2.50 × 10²" affirm them, "250" leaves them hanging. Conventions decide, not intuition.
Check it in the tool · Significant figures, counting, rounding and calculation rules →Read backwards, a colour code gives another plausible resistance.
Red-red-black-brown also reads the other way. The reliable landmark: the tolerance band, gold or set apart, goes on the right before reading.
Check it in the tool · Resistor colour code, reading and lookup →Browse by field
Browse the full catalogue →Tools to discover
- 2×2 and 3×3 matrices: determinant, inverse, systemDeterminant, inverse, transpose, products AB and BA, and linear system solving, with singularity detected at a relative threshold.
- Archimedes’ buoyancyFloats or sinks, submerged fraction, buoyant force on a volume and apparent weight under the fluid, with the usual fluids preset.
- Beer-Lambert law calculator (A = ε × l × c)Calculate absorbance, molar extinction coefficient, path length or concentration (A = ε × l × c).
- DNA primer melting temperature (Tm)Calculate a DNA primer's Tm with the nearest-neighbor thermodynamic model (SantaLucia, 1998), with the classic empirical formulas shown for comparison.
- Convert Mbps to MB/s (real Internet speed)Convert an Internet speed advertised in megabits per second (Mbps) to megabytes per second (MB/s), the real speed shown by your downloads.
- Convert bar to psiConvert a pressure from bar to psi (pound-force per square inch) and back, with the exact factor and a tire/hydraulics example.
- AWG gauge: diameter, section and metric equivalentConvert an AWG gauge to diameter and cross-section, or a diameter in mm to the closest AWG, by the exact formula of the standard.
- 4-20 mA scalingConvert a physical quantity to a 4-20 mA loop current and back, reversed scale included, with faults flagged.
Why an instrument rather than an AI?
Everything this site does, a generative AI can roughly do. Here is what "roughly" costs, and what an instrument guarantees.