Bill of Quantities in Construction
A practical guide for construction firms and tradespeople: how to build a bill of quantities, link quote, execution and invoicing, and stop losing money on it
A bill of quantities is the heart of every construction job. It's a list of items with a unit, quantity, and price that a firm tenders, budgets, executes, and invoices by. When it's good, you can always say how much is done, how much is left, and whether you're in the black. When it's loose and undisciplined, disputes over variations and the gap between quote and invoice eat your margin. In this article you'll find how to build one, how to link it from a price quote through execution to the invoice, a model example, and honest limits. Try Bidmio.
Why a bill of quantities matters more than it seems
Many firms treat the bill of quantities as a tender formality. In reality it's the one document that follows you through the entire job – from the first estimate to the last invoice. If it's tidy, you control the budget, the progress, and the invoicing. If it isn't, every vague item is a potential dispute with the client and lost margin. With margins that in construction rarely exceed 10%, it's exactly the accuracy of the BoQ that decides the profit.
Four reasons to do the BoQ properly
1It's the basis for the price
The whole quote is built on the bill of quantities. An error in a quantity or a forgotten item flows straight through as a loss on the job.
2It holds the job together
You use the same list of items in the quote, during execution, and on the invoice. One source of truth means less confusion and fewer disputes.
3It makes progress measurable
With items and quantities, you can always say what percentage is complete and how much still needs to be finished and invoiced.
4It protects against disputes
A clear description and unit are your defence. When an item is precise, the client can't claim they expected something else.
What a bill of quantities is and what it's made of
A bill of quantities (also called a priced item list or itemized work list) is a structured list of all the work and materials a job needs. Each item has its description, unit, quantity, and price. A good BoQ isn't a pile of lines in Word – it has a logical structure, discipline in its units, and descriptions a colleague who wasn't at the site visit can still understand.
When these four elements line up, the bill of quantities stops being a tender document and becomes a management tool. That's exactly what makes it the link between quote, execution, and invoice.
The four building blocks of a good bill of quantities
- Structure and item codes: Items split into logical sections (e.g. demolition, masonry, plastering, electrical) with a code or number so you can navigate them.
- An unambiguous item description: A specific description including material, thickness, or finish – not just „tiling“, but „wall tiling, 30x60 format, flexible adhesive“.
- Unit and quantity: Each item has a clear unit (m2, m3, lm, pcs, hrs) and a precise quantity measured from the drawing or on site, not eyeballed.
- Unit and total price: Price per unit times the quantity gives the item's price. The sum of items is the job's price, from which you can read the margin.
How the BoQ links quote, execution, and invoicing
The value of a BoQ shows in full when you stop building it three times from scratch. Here are seven ways one bill of quantities drives the whole job. The numbers are indicative estimates from everyday practice.
1The BoQ as the basis of the quote
The quote comes out of the bill of quantities in one move. In the price quotes module you add unit prices and margins to the items and the quote is ready. No copying the list into a spreadsheet and back.
📊 Time saved: from 60-120 minutes per quote to 15-30 minutes of editing items.
2From quote straight into execution
When the client approves the quote, the same BoQ becomes the work plan. In project management you assign items to phases and people, so everyone knows what and how much to do.
📊 Impact: one list of items instead of three independent documents.
3Measuring progress against the BoQ
For each item you record how much is done. That gives you a real completion percentage for the job and a basis for interim invoicing – not a feeling of „we're about halfway“.
📊 Impact: a precise view of the job's status anytime, not once a month.
4From the BoQ straight to the invoice
You carry finished items over to the invoice via the invoicing module. The invoice then matches exactly what was quoted and what was actually done – the end of gaps between quote and invoice.
📊 Impact: the invoice matches the quote item by item.
5Interim invoices and retention by the BoQ
On larger jobs you invoice progressively by completed items. In online invoicing you issue an interim invoice with a completion percentage and retention, without manual maths.
📊 Impact: faster cash flow and a clear view of what's already invoiced.
6Variations as an extension of the BoQ
When a change comes in, you don't add it outside the system on a scrap of paper. You add it as a new item to the BoQ with its own approval, so the variation is recorded, agreed, and invoiced.
📊 Impact: fewer forgotten variations and disputes over what was agreed.
7Budget vs actual comparison
At the end (and during) the job you compare the planned prices from the BoQ with the actual costs. You immediately see which items were underpriced and where you really made the margin.
📊 Impact: a lesson for the next quote and more accurate estimates.
A model example: a flat renovation by the BoQ
An illustrative example of a smaller firm (flat renovations, 6 people) on a job of roughly EUR 28,000. The numbers are indicative and meant to show where the BoQ decides the profit.
Model firm: 6 people, flat renovations
Loose list in a spreadsheet
Quote: a list of items in Word, some descriptions vague.
Execution: the BoQ wasn't used, progress only guessed.
Variations of ~EUR 2,200 undocumented, some unpaid.
Invoicing: the invoice didn't match the quote, arguing with the client.
Disciplined BoQ in Bidmio
Quote: items with units and quantities from one source.
Execution: progress measured item by item, a clear % complete.
Variations approved and invoiced, no loss.
Invoicing: interim invoices match the quote item by item.
Model result: variations of ~EUR 2,200 captured, shorter arguing at handover, and an invoice that matches the quote exactly. On a single job that's the difference between a tight break-even and a healthy margin.
5 bill of quantities mistakes that cost money
Most disputes and lost margins arise not on site but in a badly built bill of quantities. Here are the most common mistakes and how to avoid them.
1Loose, ambiguous item descriptions
⚠️ Causes:
- •An item like „bathroom tiling“ with no format, adhesive, or height.
- •The assumption that „we understand each other anyway“.
✅ Solutions:
- Always state the material, dimension, and method in the description.
- Use template items that have the description ready and you just fill in.
2No discipline in units
⚠️ Causes:
- •Sometimes m2, sometimes pcs, elsewhere a lump sum with no unit.
- •Mixing material and labour into one item.
✅ Solutions:
- Set one unit per type of work and stick to it.
- Separate labour and material so prices can really be compared.
3Mismatch between quote and invoice
⚠️ Causes:
- •The invoice is written from scratch, not from the quote's items.
- •Changes during execution aren't carried into the BoQ.
✅ Solutions:
- Invoice straight from the BoQ's items, not from memory.
- Record every change in the BoQ before you issue the invoice.
4Quantities eyeballed
⚠️ Causes:
- •Quantities rounded off without measuring from the drawing.
- •Pressure to submit the quote fast.
✅ Solutions:
- Measure quantities from the drawing or on site, even if it takes longer.
- When unsure, add a reserve and state it transparently.
5Variations outside the BoQ
⚠️ Causes:
- •Changes agreed verbally on site.
- •There's no approval step for additional work.
✅ Solutions:
- Add every variation as an item with its own approval.
- Don't start a variation without the client's agreement.
How to start doing BoQs properly in 30 days
You don't have to rebuild the whole firm. This plan takes you from chaotic spreadsheets to a BoQ that holds the job together.
1.Week 1: Tidy up your items
Goal: to have a library of items you use over and over.
- List the 30-50 items you do most often.
- Add a precise description and unit to each one.
- Add an indicative unit price from the last job.
📋 A library of items with consistent descriptions and units.
💡 Start with the items that repeat on every job – that's where you save most.
2.Weeks 2-3: Build one whole job from the BoQ
Goal: to run the full cycle on one real job.
- Build the BoQ and create a quote from it.
- Record completed quantities item by item during execution.
- Issue an interim invoice straight from the completed items.
📋 One job run from BoQ through quote to invoice.
💡 Pick a medium job – a small one shows nothing, a big one is a risk.
3.Week 4: Evaluate and set a rule
Goal: compare plan and reality and make the BoQ the standard.
- Compare the planned prices from the BoQ with the actual costs.
- Add the missing items to the library.
- Set the rule: no quote and no invoice outside the BoQ.
📋 An evaluated margin and the BoQ as a company standard.
💡 Even one better-captured variation per job pays for the whole change.
What a bill of quantities won't do for you
The BoQ is a powerful tool, but not a miracle. So you don't expect the impossible, it's worth knowing its limits. The best bill of quantities is only as good as the data and decisions you put into it.
4 things that stay with you
1It won't replace knowing prices
The BoQ totals what you enter. Whether the unit price is realistic and the margin sustainable is your call, based on experience and the market.
2It won't measure the quantity for you
Quantities have to be measured from the drawing or on site. A wrong input gives a wrong budget, however neat the BoQ looks.
3It won't settle the deal with the client
A disciplined BoQ eases disputes, but it doesn't replace a clear contract and approval of variations. That's still up to people.
4It won't cover the unexpected
Hidden defects, poor ground, or design changes aren't foreseen by the BoQ. That's why room for variations and a reserve matter.
How Bidmio handles bills of quantities
In Bidmio the bill of quantities isn't an isolated spreadsheet. It's one list of items that travels through the whole job – from quote through execution to invoice – and everywhere you see the same numbers.
| Module | Description | Benefit |
|---|---|---|
| Price quotes | You build the BoQ with items, units, and prices in the price quotes module, and the quote comes out of it instantly. | From one list straight to a professional quote, no retyping. |
| Project management | You assign the BoQ's items to phases and people in project management and track their completion. | A real completion percentage for the job anytime. |
| Invoicing module | You carry finished items over to the invoice via the invoicing module exactly by the BoQ. | An invoice that matches the quote item by item. |
| Online invoicing | Interim invoices, retention, and completion percentage you issue in online invoicing. | Faster cash flow and a clear view of what's invoiced. |
| Item library | Frequently used items are stored with description, unit, and price, so a new BoQ comes together in minutes. | Faster, more consistent BoQs across jobs. |
| Variations and changes | You add additional work as items with their own approval, so they're recorded and invoiced. | Fewer forgotten variations and disputes with the client. |
Frequently Asked Questions
A good BoQ is the insurance on your margin
A bill of quantities isn't a tender formality but a tool that holds the job together from the first estimate to the last invoice. When it has discipline in its units, unambiguous descriptions, and lives in one system, disputes stop arising and the invoice matches the quote. Bidmio links the BoQ from the price quote through project management to invoicing. Try it on your own job.
Try Bidmio for free and build BoQs that protect your margin.
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