= Microplate
A <microplate> is a tray containing an ordered array of small wells that keep samples physically separate while permitting repeatable handling and measurement. A <microplate reader> addresses wells to measure optical signals. The plate is consequently part of the measurement geometry: its positioning, well shape and material affect how illumination reaches the solution and how transmitted or emitted light is collected.
The <microplate footprint> is the base outline used to fit the plate into handling equipment. The primary footprint standard specifies nominal length127.76mm and width85.48mm. Its tolerances distinguish measurements within12.7mm of the corners, $\pm0.25\,\mathrm{mm}$, from measurements anywhere along the sides, $\pm0.5\,\mathrm{mm}$. The stated dimensions apply at $20\,{}^{\circ}\mathrm C$ unless otherwise specified.<Microplates - Footprint Dimensions by SLAS>[§1.2 and §4.1.1.1–4.1.1.2, reference temperature and footprint tolerances]{ref} Nominal dimensions alone therefore do not define the entire fit envelope.
For an original counting and volume example, an8-row,12-column layout has96 wells. Filling each with200µL requires19.2mL of delivered liquid, before losses in transfer equipment are included. Equal delivered volume does not itself prove equal concentration, and a plate-wide mean can conceal an individual underfilled well. Keeping the row/column address with each reading allows sample, reference and repeat locations to remain distinguishable.
For an ideal flat-bottom well, a volume estimate can be related to depth by $\ell=V/S$, where $S$ is its internal liquid-covered area. A hypothetical $S=32\,\mathrm{mm^2}$ and $V=160\,\mathrm{mm^3}=160\,\mathrm{\mu L}$ give5mm depth. Curved bottoms, taper and the meniscus alter that simple geometry. In transmission measurements the resulting depth enters the <Beer-Lambert law>, making <microplate path-length correction> relevant to comparisons across filling volumes.
The standard's foreword records dimensional variation across suppliers as a source of problems in automated instruments and describes standardization work beginning in1995.<Microplates - Footprint Dimensions by SLAS>[Foreword, dimensional incompatibility and initial standardization work]{ref} A common footprint promotes mechanical compatibility; it does not imply identical well volumes, optical backgrounds or spectral transmission. Those properties still need to match the intended physical measurement.
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