At MeasuredHome, we want our calculators to give you useful estimates that you can rely on when planning a project.
Getting a number on the screen is the easy part. Making sure that number has been calculated properly takes considerably more work.
Before we publish a calculator, we check the maths behind it, the measurements and conversions it uses, the assumptions built into the calculation and the way the calculator behaves when someone actually uses it.
Because MeasuredHome is focused on UK building and home improvement, we also try to base our calculators on materials, sizes and construction methods that make sense for UK projects.
Here is how we test them.
We check the maths independently
One of the most important parts of our testing is simple: we do not use the calculator’s own answer to decide whether it is correct.
We work out what the result should be separately and compare that with the result produced by the calculator.
Depending on the calculator, this can involve checking things such as:
- Areas and volumes
- Material quantities
- Coverage rates
- Percentages and wastage
- Ratios
- Metric and imperial conversions
- Rounding
- Calculations involving several stages or inputs
For more involved calculations, we also use independent computational checks to verify the arithmetic.
This matters because a calculator can appear to work perfectly while still containing an error in its formula or code. An independent result gives us something reliable to compare it against.
We check the assumptions behind the numbers
Good maths does not automatically make a good building calculator.
Many construction calculations depend on assumptions about the materials or methods being used. These might include the dimensions of a brick or block, mortar joint thickness, material density, coverage rates, spacing, wastage or the amount of material needed for backfill.
We review these assumptions separately from the maths.
Where suitable information is available, we prefer UK sources such as government guidance, recognised industry and professional organisations, standards information and technical information published by manufacturers.
There is not always one correct figure.
Building materials vary between manufacturers and projects vary enormously. Ground conditions, installation methods and the products being used can all affect the amount of material required.
When a value is intended to be a typical or representative figure, rather than something that applies universally, we try to make that clear.
We check units and conversions
A surprising amount can go wrong when measurements are converted from one unit to another.
Where a calculator uses different units, we check the conversion separately and make sure the correct units are being used throughout the calculation.
For calculators that support both metric and imperial measurements, we also test equivalent measurements to make sure they produce equivalent results.
A measurement entered in feet and inches should represent the same physical measurement when entered in metres or millimetres.
There can occasionally be a very small difference in what is shown because displayed values need to be rounded, but changing measurement systems should not change the underlying calculation.
We check rounding carefully
Rounding is particularly important when calculating building materials.
There is often a difference between the exact mathematical result and the quantity you actually need to buy.
For example, a calculation might show that a project requires 48.2 blocks. In practice, you cannot buy 0.2 of a block, so the purchasing quantity needs to be handled appropriately.
We check where rounding takes place and make sure values are not rounded too early in a calculation.
Where materials have to be purchased as whole items, we also check that the calculator does not accidentally round the required quantity down.
We test the calculator itself
Checking the formula is only part of the job.
The calculator also needs to work properly for the person using it.
We test the important controls and options available in each calculator. Depending on the tool, this might include changing measurements, choosing different materials, switching between metric and imperial units, entering optional information, changing advanced settings, calculating a result and resetting the calculator.
We also check what happens when something is entered incorrectly.
Required fields should behave as expected, invalid measurements should be caught where appropriate and error messages should disappear once the problem has been corrected.
We also look for obvious technical problems such as broken controls, results that fail to update, old results remaining on screen or values such as NaN, Infinity or undefined appearing in the results.
We test unusual inputs too
Most people will use our calculators with ordinary measurements, but unusual values can expose problems that normal examples do not.
Where it is relevant, we test things such as zero values, invalid measurements, very small quantities and values close to points where a result should round up or change.
We do not enter hundreds of slightly different numbers simply for the sake of doing more tests.
Instead, we identify the different rules used by a calculator and choose tests that exercise those rules. If several inputs use exactly the same calculation, repeatedly testing the same logic with different numbers tells us very little.
The aim is to find problems, not to inflate the number of tests performed.
If something looks wrong, we investigate it
When a calculator produces a result that does not match our expected result, we investigate the difference.
We do not change the expected answer simply because the calculator produced something else.
The cause could be the formula itself, the way it has been implemented, a unit conversion, rounding, an input validation rule, an assumption or simply the way a result is being displayed.
Once the cause has been identified and corrected, we test that part of the calculator again. We also check anything directly affected by the change.
We do not automatically repeat every previous test after a small change if those parts of the calculator could not have been affected.
How we check construction information
Some things can be proved mathematically. Others cannot.
If a room measures 4 metres by 5 metres, its area can be independently calculated as 20 square metres.
A statement such as how much wastage should be allowed for a particular material is different. There may be a sensible typical allowance, but the right amount can depend on the material, layout, installation method and the project itself.
We keep this distinction in mind when reviewing our calculators.
For construction specific information, we look for suitable supporting evidence rather than relying on the arithmetic alone. We favour UK information where possible and may use government guidance, standards information, professional or industry organisations, established technical references and manufacturer documentation.
Manufacturer figures are treated with care. A specification for one manufacturer’s product does not necessarily apply to every similar product on the market.
Where there is genuine variation, we would rather acknowledge it than give a figure a level of certainty it does not deserve.
Estimates and real projects
Our calculators are designed to help with planning and estimating. They cannot account for every circumstance that might affect a real building or home improvement project.
Actual requirements can vary because of the product you choose, site conditions, cutting and breakage, installation methods, workmanship, ground conditions and other factors specific to the job.
Some projects also involve structural, safety or regulatory requirements that cannot be determined by a general online calculator.
MeasuredHome calculators should not be used as a replacement for structural calculations, professional advice, manufacturer instructions or any approvals or requirements that apply to your project.
For significant material purchases, it is always sensible to check the final quantity against the specifications of the products you intend to use before ordering.
What we mean when we say a calculator has been tested
Testing a calculator does not mean entering every possible combination of numbers.
That would not necessarily make the calculator more reliable.
Instead, we identify the important calculations, conversions, assumptions, validation rules and functions within the tool. We then test representative cases that allow us to check whether those parts are working as intended.
If two situations use the same underlying calculation, proving that calculation works is normally more useful than repeating the same test many times with slightly different values.
More complicated calculators naturally need more testing than simple ones.
A calculator is considered ready when its important calculation paths have been checked, its main functions behave correctly and any problems found during testing have been resolved or clearly accounted for.
We continue to review our calculators
Publishing a calculator does not mean it can never change.
We may review a calculator when we add new features, change its calculation method, update an assumption or find something that could be improved.
When a change affects the calculation or an important part of the calculator’s behaviour, we check the affected parts again.
We also welcome reports from people using our tools.
If you think you have found an incorrect result, please contact us and tell us which calculator you were using, what values you entered and what result you received. That gives us the information we need to reproduce the calculation and investigate it.
A final word about accuracy
We put a lot of care into checking the calculators published on MeasuredHome, but no general building calculator can know everything about a particular project.
Our aim is to provide calculations that are mathematically sound, based on reasonable and clearly understood assumptions, and useful for real world planning.
The results should still be treated as estimates where real world conditions or product specifications can affect the final quantity.
For more information about the appropriate use of our tools and their limitations, please read our Calculator Disclaimer.