96 Well Plate Dimensions (ANSI/SLAS Standard)

A standard 96-well microplate measures 127.76 mm x 85.48 mm at its base (5.03 in x 3.37 in), stands about 14.35 mm tall, and holds its wells in an 8-row by 12-column grid with the well centres 9 mm apart. Those numbers come from three ANSI/SLAS microplate standards, and they are what lets one plate fit a reader, a washer, a stacker and a liquid-handling robot. This page lays out each dimension, the tolerance behind it, and the fixed point (well A1) that automation is taught from.

Who uses this: lab technicians and core-facility staff setting up readers or robot decks, instrument and consumables buyers comparing plate specifications, and students learning what “SBS format” means. For what a microplate is and what it is used for, see What Is a Microplate?.

What the 96-well plate standards fix

Three published standards define the physical geometry of a microplate. Each is a short document from SLAS (the Society for Laboratory Automation and Screening), reaffirmed as ANSI/SLAS 1-2004 (R2012), 2-2004 (R2012) and 4-2004 (R2012):

ANSI/SLAS 1-2004, Footprint Dimensions: the outside length and width of the plate base.
ANSI/SLAS 2-2004, Height Dimensions: the overall height of the plate.
ANSI/SLAS 4-2004, Well Positions: where the well centres sit for 96-, 384- and 1536-well plates.

The SLAS standards page lists two further documents, ANSI/SLAS 3-2004 (Bottom Outside Flange Dimensions) and ANSI/SLAS 6-2012 (Well Bottom Elevation), which are outside the scope of this page. The standards began as an effort by the Society for Biomolecular Screening (SBS) from 1995 because plate dimensions varied between and within vendors, which caused problems in automated instruments; SBS merged with the Association for Laboratory Automation in July 2010 to form SLAS. That history is why you will see both “SBS format” and “ANSI/SLAS” used for the same footprint.

Footprint: length, width and corner radius

The 96-well plate footprint is 127.76 mm long by 85.48 mm wide, measured at 20 °C (68 °F). The tolerance is tighter near the corners than along the sides, a detail that is often collapsed into a single “±0.5 mm” in summaries.

Dimension	Within 12.7 mm (0.5 in) of the outside corners	At any point along the side
Length	127.76 mm ± 0.25 mm (5.0299 ± 0.0098 in)	± 0.5 mm (0.0197 in)
Width	85.48 mm ± 0.25 mm (3.3654 ± 0.0098 in)	± 0.5 mm (0.0197 in)

Two more requirements in ANSI/SLAS 1-2004: the footprint “must be continuous and uninterrupted around the base of the plate”, and the outside corners of the bottom flange have a radius of 3.18 mm ± 1.6 mm (0.1252 ± 0.0630 in). The standard defines the minimal dimensions a microplate must meet to be considered compliant, so it does not describe every feature of a given vendor’s plate.

Height and stacking

ANSI/SLAS 2-2004 gives a plate height of 14.35 mm (0.5650 in). The tolerance depends on how height is measured: ± 0.25 mm (0.0098 in) to the maximum protrusion of the perimeter wells, and ± 0.76 mm (0.0299 in) for overall height. The plate’s top stacking surface may project no more than 0.76 mm (0.0299 in) above the nominal height, and the top surface must be parallel to the resting surface within 0.76 mm.

The standard offers two options, and makers who advertise compliance must clearly state which they meet:

Part 4.1, typical height with clearance: adds a minimum clearance of 1 mm (0.0394 in) between the resting plane and the bottom external surface of the wells, limited to the well area.
Part 4.2, typical height: the same height dimensions without that clearance requirement.

Well layout and the position of A1

ANSI/SLAS 4-2004 (part 4.1) arranges the 96 wells in 8 rows by 12 columns, with a constant centre-to-centre spacing (pitch) of 9 mm (0.3543 in) in both directions. Positions are measured from the outside edges of the plate:

The centre of the first column is 14.38 mm (0.5661 in) from the left outside edge.
The centre of the first row is 11.24 mm (0.4425 in) from the top outside edge.
Each following column and row is a further 9 mm along.
Each well centre must sit within a 0.70 mm (0.0276 in) diameter true-position tolerance.

The standard also requires the top-left well to be marked distinctively, for example with the letter A or the numeral 1 on the left side, or the numeral 1 above. This is why “A1” is the reference corner when you orient a plate in a reader or teach a robot a deck position.

Because the layout is symmetric, simple arithmetic on the standard’s numbers gives the far corner: the last column centre is 14.38 mm + 11 x 9 mm = 113.38 mm from the left edge, and the last row centre is 11.24 mm + 7 x 9 mm = 74.24 mm from the top edge. These two figures are calculated here from the standard’s values, not quoted from it.

96 vs 384 vs 1536: well geometry side by side

ANSI/SLAS 4-2004 defines three well-position parts that share the same footprint and differ in grid and pitch. The values come from the standard.

Format (part)	Layout	First column centre from left	First row centre from top	Pitch	Position tolerance
96-well (4.1)	8 rows x 12 columns	14.38 mm	11.24 mm	9 mm (0.3543 in)	0.70 mm
384-well (4.2)	16 rows x 24 columns	12.13 mm	8.99 mm	4.5 mm (0.1772 in)	0.70 mm
1536-well (4.3)	32 rows x 48 columns	11.005 mm	7.865 mm	2.25 mm (0.0886 in)	0.50 mm

Halving the pitch each time quadruples the well count on the same footprint. For working volumes per well and vessel surface areas, which these standards do not specify, see 384-Well Plate Volume and Cell Culture Reference Numbers.

What to check on a plate or instrument spec sheet

The standards themselves state two checks that a buyer or instrument operator can apply:

Which parts are claimed. The height standard requires advertisers to state whether they meet part 4.1 or 4.2, and the well-position standard requires them to state which of the 96-, 384- or 1536-well parts they meet. A spec sheet that says only “SBS compliant” leaves both questions open.
Which dimensions are covered. ANSI/SLAS 1-2004 sets minimal footprint dimensions at 20 °C. It says nothing about well volume, well diameter or depth, or plate material, so those must come from the manufacturer’s own specification.

Common mistakes

Treating “96-well” as a complete specification. The well count says nothing about height option (4.1 or 4.2), well volume or well bottom.
Applying the ± 0.5 mm side tolerance everywhere. Within 12.7 mm of the corners the footprint tolerance is ± 0.25 mm.
Orienting by eye instead of by A1. The marked top-left well is the reference for positions in the standard.
Mixing up pitch and well diameter. The 9 mm figure is centre-to-centre spacing, not the width of a well.

Frequently asked questions

How big is a 96-well plate?

The standard footprint is 127.76 mm x 85.48 mm (5.03 in x 3.37 in) with a typical height of 14.35 mm (0.565 in), per ANSI/SLAS 1-2004 and 2-2004.

What is the well spacing on a 96-well plate?

9 mm (0.3543 in) centre to centre, in both rows and columns, per ANSI/SLAS 4-2004.

Are all 96-well plates the same size?

Plates that meet the standards share the footprint and well positions, within the stated tolerances. The standards define minimal dimensions, and features they do not cover, such as well volume and depth, vary by product. Check which parts of the standard a manufacturer states it meets.

What is the difference between ANSI/SBS and ANSI/SLAS?

They name the same family of microplate standards. The work started at the Society for Biomolecular Screening (SBS), which merged with the Association for Laboratory Automation in July 2010 to form SLAS. SLAS notes that it is not itself a standardizing organization; the standards are published as ANSI/SLAS documents.

Which dimension should a plate reader or robot be taught from?

Well A1, the marked top-left well, 14.38 mm from the left edge and 11.24 mm from the top edge. See also What Is a Plate Reader? and Multimode vs. Single-Mode Plate Reader.