Why these exist
Most of our tools show a formula and a result in one line, which is exactly what you want when you already know the units. The awkward cases are different: two sources give different conversion factors, a recipe assumes a cup that is not the cup you own, or a rule of thumb gets presented as a measurement. Those cases do not fit in a calculator, so they get an article instead.
Each guide is written from a specification in the same way a tool is: the reference values are named, the ranges that cannot be exact are labelled, and anything we could not verify is either left out or flagged. The methodology page describes that process in detail.
Published guides
- How much does a cup of flour weigh? — why the same cup holds anything from 110 g to 190 g, where the "200 g per cup" figure comes from, which bakes notice the difference, and how to measure flour when you have no scale. Pairs with the grams-to-cups converter.
- How to choose a monitor resolution — how PPI is calculated, a PPI table for 21.5" to 34" panels, why a 460 PPI phone and an 80 PPI television both look sharp, and what operating-system scaling does to your choice. Pairs with the screen size and aspect ratio tools.
- Why SAT and ACT scores don't convert exactly — how the 2018 concordance tables were built from students who took both tests, why a 1350 SAT maps to a 29 ACT while 29 maps back to 1340, and what colleges actually do with the two scores. Pairs with the SAT to ACT converter.
- How extra mortgage payments really work — why the same $100 a month saves $53,000 if you start in month one and only $19,700 if you start ten years later, what "biweekly" actually changes, and what to verify before sending extra money. Pairs with the early payoff calculator.
- Why a tin of paint covers less than its label claims — the coverage figure assumes a smooth primed surface in one coat; a real room adds a second coat, absorbs the first, and subtracts nothing for texture. Includes the allowance table and a worked 12 × 14 ft example. Pairs with the paint calculator.
- How a cold ferment really works — why a fridge ferment is not simply "slower": gas production nearly stops while enzymes and bacteria keep working, so 48 hours tastes different from 4 and 96 hours usually fails. Pairs with the pizza dough calculator.
- What actually drives a household water bill — a shower costs about 22 cents of water and 31 cents of heat, so heating beats volume for anything hot. Includes a family-of-four breakdown and why a running toilet can out-waste every shower in the house. Pairs with the shower water calculator.
Planned
In preparation: what a tyre's load and speed rating actually constrains, and how to size a home battery against real consumption rather than nameplate output.
Suggest one
If a calculator has surprised you — a result you did not expect, or two sources that disagree — that is usually a good guide topic. Tell us through the contact page.