= Microplate footprint
The <microplate footprint> is the base outline used to locate a <microplate> in a carrier, gripper or <microplate reader>. It defines a mechanical interface rather than the liquid volume or the detailed geometry of individual wells. A common nominal rectangle promotes compatibility, but its dimensional tolerances and measurement locations must accompany the nominal values.
The primary footprint standard gives length127.76mm and width85.48mm. Within12.7mm of the outside corners, its specified tolerances are $\pm0.25\,\mathrm{mm}$; measured anywhere along the sides, they are $\pm0.5\,\mathrm{mm}$. Its default dimensional reference temperature is $20\,{}^{\circ}\mathrm C$.<Microplates - Footprint Dimensions by SLAS>[§1.2 and §4.1.1.1–4.1.1.2, reference conditions and measurement locations]{ref} Using the tighter near-corner tolerance for every location would misread the specification.
For an original rectangular-envelope calculation, take a carrier opening128.40mm long and86.10mm wide. The standard's full-side upper limits are128.26mm and85.98mm, leaving total length and width clearances0.14mm and0.12mm. If the plate and opening are centered in this simplified model, those become0.07mm and0.06mm per side. Designing only from nominal dimensions would instead suggest much larger total clearances0.64mm and0.62mm.
The calculation concerns the stated planar envelope. Corner shape, flange geometry, vertical clearance, positioning features and the carrier's own tolerances can also determine whether a real plate seats correctly. The footprint standard separately specifies a continuous base outline and corner-radius requirements, rather than reducing the entire interface to two nominal lengths.<Microplates - Footprint Dimensions by SLAS>[§4.1.1.3, continuous footprint; §4.1.2, corner radius]{ref}
A footprint check can use calibrated dimensional measurements at the specified locations and conditions. It should distinguish a length measurement from a functional fit test: a plate that enters one carrier does not by that observation alone establish every standard dimension, and agreement in two measured dimensions does not establish optical suitability. Well-bottom transmission and <microplate path-length correction> remain separate parts of the optical measurement chain.
The standard's foreword identifies dimensional variation between suppliers as an automation problem. This supplies the practical motivation for the interface: a plate should arrive at a predictable physical location so that downstream handling and measurements can be repeatable.<Microplates - Footprint Dimensions by SLAS>[Foreword, dimensional variation and automated-instrument compatibility]{ref}
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