Work Size vs Coordinating Size: Where Brick Quotes Break

Work size vs coordinating size is the 10 mm that decides whether your brick quote and the architect's drawing describe the same wall. One number is the brick you actually fire, palletise and ship. The other is the space that brick takes up once it has mortar around it. Publish only one of them and somebody downstream guesses the other — usually wrong, usually after the container has sailed.

This is not a rounding argument. On a window opening it is the difference between a brick that fits and a brick that gets cut on site at your buyer's cost.

Work size vs coordinating size, defined

Three different dimensions describe the same brick, and every one of them is correct in its own context.

Work size is the dimension the manufacturer declares for the brick itself, with no mortar included. In the UK the most widely used work size for clay bricks is 215 × 102.5 × 65 mm.

Coordinating size is the work size plus the mortar joint allowance — the space one brick occupies in the finished wall. With a nominal 10 mm joint, the Brick Development Association gives the UK coordinating size as 225 × 112.5 × 75 mm.

Actual size is what comes out of the kiln. Clay shrinks, and it does not shrink identically across a batch, so the declared work size is a target that real bricks land near, not on. How near is set by the tolerance and range categories declared under EN 771-1.

The trap is that both parties in a transaction usually publish one number and assume the other. A quotation that says "215 × 102.5 × 65" and a drawing that says "225 coursing" are describing exactly the same product — but only somebody who already knows the system can see that. For the full set of market-by-market figures, the standard brick dimensions reference lists the common formats side by side.

The brick dimension block: eight fields worth publishing

This is the block to paste into a specification, a quotation, or the dimension panel of a product drawing. It takes about six lines and removes most of the back-and-forth.

Fields 1 and 6 are the two everyone argues about. Fields 3, 4 and 5 are the ones that make 1 and 6 defensible.

How to fill each field

Fields 1 and 2: work size and the standard it is declared to

Write the work size in the order your buyer's market reads it, then name the standard. Under BS EN 771-1 the manufacturer declares the work size; under the American system the equivalent is the specified dimension, which Brick Industry Association Technical Note 10 defines as "the anticipated manufactured dimensions of the brick, without consideration for mortar, which are to be used in project specifications and purchase orders."

Never publish a coordinating or nominal figure in the work-size field. It is the most common error in export brick documentation, and it survives translation into every language on the quotation.

Fields 3 and 4: tolerance category and range category

Tolerance is the difference between the declared work size and the average actual size of a sample. Range is the spread within the sample, between the largest brick and the smallest. A batch can be perfectly centred on 215 mm and still look ragged if the range is wide.

EN 771-1 defines both as declared categories. The BDA publishes the numbers for the standard UK work size:

Tm and Rm are the third option in each case: whatever the manufacturer declares, which may be tighter or looser than the categories above. Declare Tm or Rm and you must publish the number, or the declaration means nothing. A practical call: if your buyer's design calls for crisp, regular brickwork, they need the tighter categories, and they will find out one way or another. Declaring T1 up front is cheaper than discovering it on a rejected sample panel.

Fields 5, 6 and 7: joint thickness, coordinating size, coursing

A coordinating size without a stated joint thickness is a number with no arithmetic behind it. Say "10 mm nominal joint" and the reader can rebuild 225 × 112.5 × 75 from 215 × 102.5 × 65 themselves — and rebuild it correctly for a 12 mm joint if their specification calls for one.

Coursing is where errors compound. In the UK system the 75 mm coordinating height gives four courses to 300 mm. In the American system BIA Technical Note 10 publishes coursing per designation: a modular brick is 3 courses to 8 in. (203 mm), a queen or king brick 5 courses to 16 in. (406 mm). Publishing the coursing line saves your buyer from deriving it and getting it wrong on the fifth course.

Field 8: which coordinating condition the number is for

This is the field almost nobody publishes, and it is the one that decides opening sizes. The BDA sets out three conditions for any brickwork dimension:

• CO+ — brick plus two joints. Used for openings in brickwork.
• CO — brick plus one joint. Used for panels with opposite return ends.
• CO− — brick dimension only. Used for piers, or panels between openings.

State which condition your figure assumes. "225 mm (CO)" and "225 mm" are not the same information.

Worked example: UK clay brick

• Work size: 215 × 102.5 × 65 mm, declared to BS EN 771-1
• Tolerance: T2 (215 mm dimension may average 211–219 mm)
• Range: R2 (spread within a sample up to 4 mm on the 215 mm dimension)
• Assumed joint: 10 mm nominal
• Coordinating size: 225 × 112.5 × 75 mm
• Coursing: 4 courses = 300 mm
• Condition stated per dimension: CO+ at openings

Six lines, no ambiguity, and every figure traceable to a published category rather than to a sales estimate.

Worked example: US modular and non-modular brick

The American system uses different words for the same idea and adds one trap the metric system does not have: not every brick has a nominal size at all.

BIA Technical Note 10 defines nominal dimensions as "the result of the specified dimension of the brick plus the intended thickness of its intended mortar joint," landing on round 4 in. or 8 in. modules. Modular brick have all three dimension sets. Non-modular brick have specified and actual dimensions only — no nominal dimensions exist for them. Quote a nominal size for a queen brick and you have invented a number.

Notice the same designation changes size with the joint: a modular brick is 3⅝ in. wide for a ⅜ in. joint and 3½ in. wide for a ½ in. joint. The nominal 4 in. stays put. That is the reason a purchase order naming only "modular brick" is incomplete.

Tolerance works differently too. Instead of declared categories, ASTM C216 assigns permissible variation by type. Per BIA Technical Note 9A, for a specified dimension over 6 to 8 in. (152 to 203 mm), Type FBX allows ±5/32 in. (4.0 mm) and Type FBS allows ±1/4 in. (6.4 mm) from the specified dimension. Out-of-square on the exposed face is capped at 3/32 in. (2.4 mm) for FBX and 1/8 in. (3.2 mm) for FBS. Type FBA is whatever the purchaser specifies, but not more restrictive than FBS.

If the gap between declared and manufactured dimensions is new territory, the general case is covered in nominal vs actual dimensions — brick is simply the oldest and strictest example of it.

Worked example: Germany's 12.5 cm module

German masonry runs on the octametric system in DIN 4172, built on a module of 12.5 cm that covers the brick and the mortar joint, based on a 1.0 cm joint. The brick formats follow from subtracting the joint from the module:

The component dimensions — the German counterpart of CO+, CO and CO− — are published as formulas, where x is the number of bricks including joint:

• Außenmaß (external dimension) = x × 12.5 cm − 1.0 cm
• Öffnungsmaß (opening dimension) = x × 12.5 cm + 1.0 cm
• Vorsprungsmaß (projection dimension) = x × 12.5 cm

One detail from the same source is worth carrying into any dimension dispute: in practice the dimensions cannot be held exactly, so fit is recovered by squeezing or stretching the head joints — by no more than 1.5 cm. That is a published site tolerance, not an excuse. If your brick is out by more than the joint can absorb, the wall does not close.

Where quotes actually break

Almost every brick dimension dispute is a document problem, not a manufacturing problem. The brick is fine. The PDF said "215 × 102.5 × 65" and the estimator, working to a drawing that coursed at 225, assumed the quotation was already the coordinating size and ordered short.

A paragraph of explanation does not fix this, because the estimator is not reading paragraphs. What fixes it is a dimension panel on the drawing where each figure sits next to the thing it measures: the work-size arrow spanning the brick face only, the coordinating arrow spanning brick plus joint, the coursing dimension running up four courses, and the tolerance category printed beside the size it qualifies. Nobody misreads an arrow.

That is the difference between a spec diagram and a decorated photo. The dimensions on a spec diagram are the real measured ones, locked to the edges of the object in the image and exported at the size your buyer's template expects — not typed into a caption, and not produced by an image generator that can output a plausible-looking "215 mm" it never measured. A measured drawing also survives translation: an arrow labelled "225" needs no German, Polish or Spanish. A sentence explaining coordinating size needs a good translator and a patient reader. See how to label building material dimensions for the labelling conventions, and the building material spec diagram format for how the panel is laid out.

Brick dimension block checklist

• The work size is labelled as a work size (or specified size), not as a bare "size"
• The declaring standard is named: BS EN 771-1, ASTM C216, or DIN 4172
• The tolerance category is declared (T1 / T2 / Tm — with the number, if Tm)
• The range category is declared (R1 / R2 / Rm — with the number, if Rm)
• The assumed joint thickness appears next to any coordinating or nominal figure
• The coordinating size states which condition it is for (CO+, CO, CO−)
• Vertical coursing is published, not left for the buyer to derive
• For US formats, no nominal size is quoted for a non-modular brick
• The drawing shows work size vs coordinating size as two separate dimension lines

FAQ

What is the difference between work size and coordinating size?

Work size is the brick as declared by the manufacturer, with no mortar. Coordinating size is that brick plus its mortar joint allowance — the space it occupies in the wall. For the standard UK clay brick the work size is 215 × 102.5 × 65 mm and the coordinating size with a nominal 10 mm joint is 225 × 112.5 × 75 mm.

What is the coordinating size of a standard UK brick?

225 × 112.5 × 75 mm, based on the 215 × 102.5 × 65 mm work size and a nominal 10 mm mortar joint, as published by the Brick Development Association. The 75 mm height is why four courses come to 300 mm.

Is nominal size the same as coordinating size?

They do the same job in different systems. Coordinating size is the EN term; nominal size is the ASTM term, defined by the Brick Industry Association as the specified dimension plus the intended mortar joint, rounded to a 4 in. or 8 in. module. The difference that bites: non-modular American bricks such as Standard, Queen and King have no nominal size at all, only a specified size.

What does tolerance category T2 mean on a brick declaration?

T2 is the tighter of the two named EN 771-1 tolerance categories. For a declared 215 mm dimension it means the sample mean must fall between 211 and 219 mm — ±4 mm. T1 is looser at ±6 mm, and Tm means the manufacturer declares its own figure, which must then be published to mean anything. Tolerance is about the sample average; the spread between individual bricks is the separate range category, R2 or R1.

Which brick dimension should go on an export spec sheet?

All of them, labelled: work size for the purchase order and packing list, coordinating size for setting out, tolerance and range categories for incoming inspection, coursing for the elevation. The cheapest way to publish work size vs coordinating size without writing an essay is a drawing whose dimension lines measure exactly what they are labelled to measure — one arrow across the brick, one across brick plus joint, both snapped to the real edges rather than typed in by hand. It removes the assumption behind almost all of these disputes, in every language your catalogue is read in.

Sources & References

• Brick Development Association — Designing to Brickwork Dimensions, Technical Guide 2023 (work size, coordinating size 225 × 112.5 × 75 mm, T1/T2/Tm and R1/R2/Rm tables, CO+/CO/CO− conditions)
• Brick Industry Association — Technical Note 10, Dimensioning and Estimating Brick Masonry (nominal, specified and actual dimensions; modular and non-modular size tables; vertical coursing)
• Brick Industry Association — Technical Note 9A, Specifications for and Classification of Brick (ASTM C216 dimensional tolerances by type; out-of-square limits)
• ASTM C216 — Standard Specification for Facing Brick (Solid Masonry Units Made from Clay or Shale)
• Ziegel Planungstool — 2.1.2 Maßordnung: DIN 4172 octametric system, 12.5 cm module, DF/NF/2DF formats, Baurichtmaß formulas