7. Assessment and Calculation
The calculation components and their outputs.
7.1 Price Ratio Conversion
Prices quoted per hour, per gigabyte-month, and per million requests cannot be combined, but ratios formed from them can. For each product category in the comparison basket, the median price across the provider's regions is taken as the reference, and every region's price for that product category is divided by it to give a price ratio. A ratio of 1.10 describes a price ten per cent above the median for that product category, and the statement means the same thing whichever unit the underlying price was quoted in.
7.2 Relative Cost Calculation
A region's relative cost percentage is the median of its price ratios across the basket, restated as a percentage difference from the median. A positive value describes a region whose catalogue prices sit above the median region of that provider, and a negative value describes a region whose prices sit below it. The percentage is an internal value, and the cost grade assigned from it under Section 7.7 is what reaches the scorecard.
Every product category in the basket carries equal weight in that median. The score is a comparison of catalogue prices and not a projection of any customer's bill. Section 11 sets out the interpretation this requires.
7.3 Evidence Sufficiency and Suppression
A region that prices only a small share of the comparison basket would produce a median resting on too few ratios to defend. Where a region falls below the sufficiency level the methodology sets for that purpose, no cost grade is published for it and the field is left empty. The region keeps its row on the scorecard and keeps its availability grade, which does not depend on the basket.
The basket coverage percentage is recorded for every region, under Section 9.4, and is an internal value. A region scoring on most of the basket and a region scoring just above the sufficiency level both carry a cost grade, and nothing on the scorecard separates them.
7.4 Service Availability Calculation
The service availability percentage counts product categories instead of comparing prices. The eligible product categories a region prices are counted, and the total is divided by the count for the provider's most complete region, which by construction scores one hundred per cent.
It describes completeness relative to the best-stocked region of the same provider, and not relative to the provider's full theoretical catalogue or to any other provider's. The percentage is an internal value, and the availability grade assigned from it is what reaches the scorecard.
7.5 Carbon Intensity Calculation
GPX Grid produces an hourly grid carbon intensity factor for each grid. A region's figure for the scorecard is the average of the hourly factors for its grid across the previous calendar month, expressed in grams of CO₂e per kilowatt-hour. The figure averages measured and modelled grid data, and states what a kilowatt-hour drawn from that grid typically carries. The emissions of a workload follow from its own energy consumption and the GCI at the hours it ran, which the Greenpixie Methodology for Cloud Emission Measurement calculates and this score does not.
A region whose grid moves between a low-carbon night and a high-carbon evening peak takes the same figure as a region holding steady at that average, so the scorecard does not separate them. Section 11.3 states the interpretation this requires.
7.6 Water Stress Assignment
Aqueduct 4.0 publishes baseline water stress as a percentage and assigns it to five named categories, being Low below ten per cent, Low to Medium from ten to twenty per cent, Medium to High from twenty to forty per cent, High from forty to eighty per cent, and Extremely High above eighty per cent. The category Aqueduct assigns to the area matched to a region under Section 6.6 is published for that region without recalculation, under a shortened label where the scorecard layout requires one.
Those thresholds are Aqueduct's own and are fixed, so Greenpixie applies no banding and no clustering method to the water stress category. A category means the same thing in every data version, and a region's category changes only when the World Resources Institute republishes the underlying figure or when the region's match changes.
The percentage behind the category expresses total water demand as a share of the renewable supply available. A region in an Extremely High area sits where existing users already withdraw more than eighty per cent of that supply, which describes how contested the supply is and not how much water the data centre draws from it. Section 11.4 states the boundary this creates.
7.7 Grade Banding
The relative cost percentage and the service availability percentage are each assigned to one of five bands, set separately for each provider, as a region is compared only against the estate it belongs to. Each band is published as a numeric grade from 1 to 5, in which 1 is the least expensive cost band and 1 the most complete availability band. The carbon intensity figure is assigned to one of seven bands published as letters from A+ to F, set once across the regions of all three providers together, as a grid serves every data centre in its area alike. Greenpixie assigns no bands to the water stress category, for the reason given in Section 7.6.
Greenpixie sets every band boundary with Jenks natural breaks, so that boundaries fall at the gaps present in the distribution and not at round numbers chosen in advance. The boundaries used in a version are published with the scores that version produced. Greenpixie sets them again from the data of each run, so a boundary quoted from one version does not apply to another.
A grade is stored with the rest of the row and is not computed at the point the scorecard is loaded. The boundaries belong to a single version and cannot be reconstructed from a figure alone. How a grade is presented, whether as a symbol, a word, a letter, or a colour, is a display decision taken outside this methodology, so a change of presentation does not require rescoring.