A purchasing team compares two wipes at $0.045 and $0.062 per sheet and concludes the first is cheaper. A production engineer watches the line use three sheets of the first for every two of the second, and concludes the opposite. Both are right, because they are measuring different things.
Price per wipe is a purchasing unit. Cost per clean square metre is a production unit. Only one of them predicts what the line will spend next quarter.
The four inputs
The model has four lines, and none of them is hard to collect.
- Sheets per square metre. How many wipes are consumed to clean one square metre of the actual surface, including the ones thrown away half-used.
- Solvent per square metre. A more absorbent wipe can hold more solvent, which is not a saving if the solvent is expensive or if the surface is left wet.
- Labour per square metre. Time is the largest line on most benches. A wipe that needs fewer passes wins even at a higher sheet price.
- Rework and defects. Residue, lint and scratches produce rework that never appears in a consumables budget.
A worked example
Suppose a bench cleans 400 m² per week. Wipe A costs $0.045 and is used at 1.6 sheets per square metre. Wipe B costs $0.062 and is used at 1.1 sheets per square metre. Labour is charged at $28 per hour, and the task takes 0.9 minutes per square metre with A and 0.7 with B.
| Line | Wipe A | Wipe B |
|---|---|---|
| Sheets per m² | 1.6 | 1.1 |
| Wipe cost per m² | $0.072 | $0.068 |
| Labour per m² | $0.420 | $0.327 |
| Total per m² | $0.492 | $0.395 |
| Weekly, 400 m² | $197 | $158 |
Wipe B is 38% cheaper per sheet and 20% cheaper per clean square metre. The difference is almost entirely labour, which is why a sample trial that only measures sheets used will miss it.
Why the more expensive wipe wins
Better absorbency, a sealed edge and a consistent fold all reduce the number of passes. They also reduce the number of sheets discarded because the operator lost control of a floppy cloth. The effect compounds: fewer passes means less solvent, less wiping time and fewer defects found at inspection.
The counter-case is just as real. A premium wipe used on a rough industrial surface is wasted, because the surface destroys the cloth before its advantages matter. Match the reference to the task, then measure.
The line most cases miss: disposal
Used wipes leave the building as waste, and the cost is not zero. A light, bulky stream costs more to transport than its weight suggests. Solvent-laden wipes may be classified as hazardous, which changes the container, the paperwork and the collection frequency.
Compare two references on the same task and the disposal difference can be a third of the saving. A cloth that needs two sheets per square metre produces twice the waste volume of one that needs one, even if both are the same weight per sheet. A paper wipe that cannot be recycled may cost more to dispose of than a cloth that goes to a laundry — and the laundry has its own water and energy footprint.
Add a disposal line to the model: kilograms per month, the classification, and the collection charge. It is rarely the largest number, but it is the one that surprises a finance team after the switch has been approved.
Run the comparison for two weeks on one bench, count sheets and time, and inspect the surface at the same point each day. A one-day trial measures enthusiasm, not consumption.
What to put in the business case
Four numbers and one caveat. Sheets per square metre, labour minutes per square metre, defect rate, and the delivered price per sheet. The caveat is supply: a wipe that saves 20% but has a 30-day lead time needs a safety stock, and that stock has a carrying cost.
Include the switch cost as well: operator training, a revised procedure, and a validation or first-article run if the surface is critical. For a validated process, the change control is part of the cost and should be in the first-year figure.
Should I compare on price per kilogram?
Only for commodity wiping. For a controlled surface, weight does not predict absorbency, lint or passes, so it is a poor proxy for cost per clean square metre.
How many sheets per square metre is normal?
It depends on the surface and the solvent. Measure your own bench; published averages are almost always optimistic because they assume a perfect operator.
Does a pre-wetted wipe change the arithmetic?
It removes the solvent bottle and fixes the dose, which usually reduces solvent per square metre and eliminates over-wetting. Add the pack cost and the open-life limit to the model.
If you want to run the comparison, we will send two references and a one-page counting sheet for the trial.
