Why your brick quantities are wrong before anyone lays one

I am not a bricklayer. I came up on the supply side, in joinery and then stairs, surveying jobs and pricing them. So I am not going to tell you how to lay a course. Plenty of people on site are better placed for that than me.

What I will tell you is where I watched this exact mistake cost people money, over and over, from the other side of the counter. It is not a bricklaying mistake. It is a quoting mistake, and it happens weeks before anyone picks up a trowel.

Here it is: the brick is 215mm long, but nothing you price is ever 215mm.

The number that prices the job is 225, not 215

A standard UK brick has a work size of 215 x 102.5 x 65mm. That is the lump of clay. It is the number on the spec sheet and it is the number people quote at each other.

It is not the number that builds anything.

Add the 10mm mortar joint and you get the coordinating size: 225 x 112.5 x 75mm. That is the number the wall is actually built to, and it is the number every drawing is designed around. Four courses come to exactly 300mm because 4 x 75 = 300. That is not a coincidence, it is the whole point of coordinating sizes.

So when a drawing gives you a dimension, it is almost always working in 225s. When you price off the brick size instead, you are pricing a wall that does not exist.

Where the 60 bricks per square metre figure comes from

Everyone in the trade knows the 60 per square metre number. Far fewer can tell you where it comes from, which means far fewer can tell when it stops applying.

The face of one brick plus its joints is 225mm x 75mm. That is 0.016875 square metres. One square metre divided by 0.016875 is 59.26. Round up and you get 60 bricks per square metre for a single skin wall in stretcher bond.

That is the whole derivation. Two numbers you already have, one division.

It matters because now you can see what it depends on. It assumes a 10mm joint. It assumes a half brick wall. It assumes stretcher bond. Change the bond and the figure moves, because a bond with headers in it puts more bricks in the same face. Build a solid one brick wall and you are at roughly double. Go to a 15mm joint on a handmade brick and the coursing changes under you.

A number you can rebuild from first principles is a number you can defend when a client questions it. A number you half remember is one you will eventually get wrong.

The brick you order is a declared size, not an exact one

This is the part I think gets missed most, and it is the one that turned up on my side of the job rather than on site.

Under BS EN 771-1, the standard that governs masonry units, a manufacturer declares the work size of the brick and declares a tolerance category against it. There are categories for both the mean size and the range. In plain terms: the brick is allowed to vary, within limits the maker has published, and different products sit in different categories.

So 215 is a declared size with a permitted spread, not a guarantee that every brick in the pack is 215.00mm.

For most jobs that is invisible, because the bricklayer absorbs it in the joint. That is what the joint is for. It becomes very visible when you have set something out to a fixed datum, or when you are matching into existing work, or when the design has decided a run must land on a whole brick.

Why this lands on the person quoting, not the person laying

Here is the bit I actually care about, and it is why this sits on a business site rather than a technical one.

The person laying the bricks finds out about a coursing problem in an afternoon. They cut, they adjust the joint, they tell you. It gets solved on the wall.

The person who quoted the job found out about it three weeks earlier and did not notice. They took a dimension off a drawing, divided by the wrong number, and put a figure in front of a customer. The wall gets built correctly and the price was wrong from the day it was sent.

That is the shape of it. The error is silent, it is upstream, and by the time it surfaces the customer has already agreed a number in writing. You are then having a conversation about a variation on something that was your arithmetic, not their change of mind. Those are the worst conversations to have and the hardest to charge for.

I watched the identical failure in stairs for years. A rise is not a rise once you account for the finished floor. A going is not a going once the nosing is on. Same disease, different trade: a component with a joint in it does not measure the same as the component on its own, and the person pricing is the one furthest from the joint.

What I would do before a price goes out

Not a method statement. Just the habits that stop the expensive version.

• Price in coordinating sizes, not brick sizes. If you are dividing by 215, stop and check whether you meant 225.
• Rebuild the per square metre figure rather than recalling it. It takes ten seconds and it makes the assumptions visible.
• Write the assumptions on the quote. Joint width, bond, single or double skin. If the client later wants Flemish bond, the fact that you priced stretcher is on the page and the variation is a normal conversation.
• Check the openings. Openings are where coursing goes wrong, because a lintel height and a floor datum are set by the design and do not care what your brick measures.
• Ask what the brick is before you price it, not after. A handmade or reclaimed brick can behave differently from a wirecut, and the tolerance category is published.
• Add your wastage as a stated line, not as a fudge buried in the rate. If you are carrying it, say you are carrying it.

None of that is clever. All of it is the difference between a number you can defend and a number you have to apologise for.

The actual dimensions

I have deliberately not turned this into a lookup table, because we already have one and it is better than anything I would repeat here.

The full set of dimensions, coursing heights and bond patterns is on our reference card: Brick Dimensions and Bond Patterns. It is print friendly, so it can live in the van rather than on a phone.

Use the card for the numbers. Use this post for the reason your quote was wrong.