Chemistry, physics and environmental science share a page here because they share very little else — each rests on a different kind of formula, and knowing which kind you are working with is most of the battle. Chemistry calculations turn a recipe of masses, volumes and concentrations into the amount of a substance actually present. Physics calculations apply the fixed equations of classical mechanics — force, energy, momentum — that have not changed since Newton. Environmental calculations, by contrast, are estimates built from published conversion factors rather than a law of nature, and behave differently as a result.
Calculators in this section
Chemistry: concentration and how much of a reaction actually happens
A solution's concentration can be expressed as molarity (moles of solute per litre of solution) or molality (moles per kilogram of solvent), and the two are not interchangeable — molarity changes slightly with temperature because a liquid's volume expands, molality does not, because mass is fixed. Diluting a stock solution follows one identity, C₁V₁ = C₂V₂, which says the amount of solute stays constant while concentration and volume move in opposite directions. Further along the reaction itself, stoichiometry and the limiting reactant calculator answer the practical question a recipe analogy makes obvious: if a reaction needs two parts of one reagent for every one part of another, whichever runs out first caps how much product can form, regardless of how much of the other reagent is sitting unused. pH and pOH sit on a logarithmic scale — each whole step is a tenfold change in hydrogen or hydroxide ion concentration, which is why a pH of 3 is not "a bit more acidic" than a pH of 6, it is a thousand times more acidic.
Physics: fixed equations, not estimates
Every physics calculator on this page implements an equation that is exact within classical mechanics: force is mass times acceleration, momentum is mass times velocity, kinetic energy is half of mass times velocity squared. These are not approximations or rules of thumb the way a financial projection is — get the inputs right and the output is correct by definition. What trips people up is not the formula but the units feeding into it: mixing pounds with kilograms, or centimetres with metres, produces an answer that is numerically wrong while looking perfectly plausible. NASA lost the Mars Climate Orbiter in 1999 for exactly this reason — one team's software produced thrust data in pound-force seconds, another expected newton-seconds, and nobody caught the mismatch until the spacecraft was gone. The calculators here work in consistent SI units for that reason, and it is worth checking your own source figures are in the same units before comparing a result against them.
Environmental science works from published factors, not physical constants
The carbon footprint calculator is a different kind of tool from the physics and chemistry calculators on this page. There is no equation of nature that says a litre of petrol produces a fixed, unarguable amount of carbon dioxide the way F = ma is unarguable — instead it uses a published emission factor, the kind maintained by bodies such as the UK's Department for Energy Security and Net Zero or the US EPA, which is periodically revised as measurement improves and as an electricity grid's own generation mix changes. Two carbon calculators using different factors, or factors from different years, will give answers that are both defensible and different, which is not something that happens with a momentum or molarity calculation.