Methodology
What kind of number each figure is, and which ones you can argue with.
A calculator that never says what kind of number it is showing forces you to trust all of it or none of it. Here is the full classification: which figures are exact, which come from a source, and which are assumptions you can change yourself.
The seven kinds of number
1. Exact mathematical constant
Nothing was measured: it is arithmetic. The area of a circle, the ratio between two tin areas, splitting a recipe across servings. It does not expire and there is nothing to argue about.
2. Exact conversion
A legal definition, not an estimate. An inch is 25.4 mm because the 1959 international yard and pound agreement defined it so, not because anyone measured it. The same goes for the pound (0.45359237 kg), the US gallon (231 cubic inches), the International Table BTU (1055.05585262 J) and the frigorie (1 kcal/h = 1.163 W). These are used with every decimal and only rounded when displayed.
3. Figure taken from a source
Someone measured it and published it. Ingredient densities are the clearest case: each one is a published weight divided by the volume of the matching measure. The source of each figure, the date it was consulted and its limitations are in Sources and updates.
4. Editable assumption
A sensible starting value that does not come from any standard: paint coverage, the bulk density of sand, a mortar joint thickness. Three conditions always hold: the default is reasonable, the field is editable, and the assumption is written into the result. When the real figure is on the packaging, the calculator says so.
5. Rule of thumb
A practical rule that gets the order of magnitude right without replacing a formal calculation. "Between 28 and 42 BTU/h per square foot" is for checking a quote, not for signing off an installation. These rules are labelled as what they are and never dressed up as an engineering result.
6. Value entered by you
Your measurements and your prices. They are not stored, not sent anywhere and not recovered from a previous visit: every time you open a calculator the form is empty. You enter the electricity price yourself, because downloading it from somewhere would create a false sense of precision.
7. Rounding
There are two, and they are not the same thing.
- Display rounding: the mathematical result with the decimals that make sense at that scale. A teaspoon gets one decimal; a cubic metre of concrete gets two.
- Commercial rounding: what you can actually buy. Whole bags, five-litre tins, 9,000 BTU units. It is always kept apart from the mathematical result and labelled separately, because they answer two different questions: how much you need, and how much to order.
What these calculators are not
They are estimates. None of them replaces a design, an on-site measurement or a professional's judgement when the job calls for one. In HVAC, the sizing model is a simplified component model, not a standardised heat-load calculation, and every result says so.
Three things this project will not do, on principle: it does not download electricity tariffs or assume a price per kWh; it does not derive electrical consumption from cooling capacity without an efficiency figure; and it does not mix EER with SEER.
Capacity, consumption and load: three different things
This is the most expensive confusion in the trade, so it is worth being explicit.
Swipe to see the whole table
| Quantity | What it measures | Units |
|---|---|---|
| Cooling capacity | The heat the unit can remove | BTU/h, frigories/h, kW |
| Electrical consumption | The electricity it uses to remove it | W, kWh |
| Thermal load | The heat that has to leave the room | W |
English and Spanish are not the same page translated
The site localises rather than translates. The Spanish version defaults to metric, uses a decimal comma and the regional synonyms people actually say. The English version uses imperial where that is natural, a decimal point and the terminology of the English-speaking market. That is why a US cup (236.6 ml) and a metric cup (250 ml) live side by side in the same calculator: they are not the same measure.
How often this is reviewed
Unit definitions do not expire. Ingredient densities are reviewed by going back to the source table. Building values are checked against manufacturers' data sheets. In HVAC the labelling rules are watched, because those do change. The date of the last review appears on every calculator and every guide, and the block-by-block detail is in Sources and updates.