How to Price a Building Job Accurately (Without Losing Money)

Most builders price jobs from experience and gut feel. And for small, familiar jobs — a garden wall, a bathroom refit — that works well enough. But as projects get bigger or more complex, the gap between "what it feels like" and "what it actually costs" widens. That gap is where money goes to die.

This guide walks through the systematic approach to pricing a building job — the same method professional Quantity Surveyors use, adapted for contractors who want to price with confidence without hiring a QS for every tender.

Step 1: Understand the Scope

Before you measure anything, make sure you understand what's being asked. Read the drawings, the specification, any schedules. Ask yourself these questions:

What's included? Does the price need to cover demolition? Drainage? Landscaping? External works? If it's not clear, ask — don't assume it's excluded and find out later it wasn't.

What's the access like? A rear extension with a 900mm side gate for access is a very different proposition to one with open drive access. Restricted access affects scaffolding, waste removal, material delivery, and plant — all of which cost money.

What's the programme? How long will this realistically take? If the client wants it done in 8 weeks and it's a 12-week job, you either need more labour (more cost) or you need to manage expectations early.

Step 2: Take Off the Quantities

This is the core of pricing — measuring every element of the build from the drawings. It's called a "take-off" because you're taking quantities off the drawings.

Work through the project in construction sequence: substructure first (foundations, ground floor, below DPC), then superstructure (walls, floors, roof, steelwork), then envelope (windows, doors, insulation), then first fix (electrics, plumbing), then second fix and finishes.

For each item, note the quantity and unit of measurement. Blockwork in m², foundations in linear metres, concrete in m³, steelwork in kg or nr. Be precise — rounding "about 30m² of blockwork" to 30 when it's actually 38 means you're eating 8m² of material and labour on that item alone.

Step 3: Price Each Item

For each measured item, you need a rate that covers three things: materials, labour, and plant/equipment.

Materials — get current prices from your suppliers. Don't use last year's rates; material costs shift regularly. Timber, steel, concrete, and insulation have all seen price movement in the last 12 months. Add 5–10% for waste and cutting.

Labour — calculate based on realistic output rates. How many m² of blockwork can your bricklayer lay in a day? How long does a joiner take to hang a door set? Be honest with yourself — optimistic labour rates are the single biggest cause of underpricing.

Plant — scaffolding, skip hire, mixer hire, HIAB/crane costs, power tools. These are easy to forget in the heat of pricing but they add up. A scaffold on a two-storey extension for 12 weeks is £2,000–£3,500.

Step 4: Add the Preliminaries

Preliminaries — "prelims" — are the project-level costs that aren't tied to any specific trade item. They include:

Site management — your time on site, or a site manager's wages. Even if you're the builder and the manager, your time has a value.

Insurance — contractor's all-risk, public liability, employer's liability. Don't skip this.

Welfare — toilet hire, drying room, first aid. Required on any site with employees.

Temporary works — hoarding, temporary protection, propping during structural alterations.

Waste removal — skip hire or grab lorry throughout the build. A 12-week extension generates a lot of rubble.

Prelims typically add 8–15% of the build cost, depending on project duration and complexity. On a £60,000 extension, that's £4,800 to £9,000. Don't absorb these costs into your margin — price them properly.

Step 5: Apply Your Overheads & Profit

Once you've totalled the direct costs (measured work + prelims), you need to add:

Overheads — your van, your yard, your accountant, your phone, your software, your tool replacement. These costs exist whether you're on this job or not, and every job needs to contribute to covering them. Typically 8–12% of the direct cost.

Profit — what you're actually earning from doing the work. This isn't your wages (that's in the labour rates or prelims). This is the return on the risk you're taking. For competitive residential work, 5–10% is typical. For complex or high-risk projects, go higher.

Combined OH&P of 15–20% on top of direct costs is standard in the UK market. Don't feel guilty about this — it's what keeps your business running.

Step 6: Sense-Check Your Price

Before you submit, compare your total against rough benchmarks. If you're pricing a 30m² single-storey extension and your total comes out at £35,000 — something's missing. If it comes out at £120,000 for a standard spec — you've over-priced something.

Cross-reference against cost per m² guides, talk to other contractors you trust, and look at any similar jobs you've done recently. The final price should feel right based on experience, but be backed by measured quantities and current rates.

Common Pricing Mistakes

Pricing from memory — "the last extension I did was £45k so this one should be about the same." No two projects are the same. Different foundations, different steel, different spec. Measure it properly.

Forgetting the small stuff — sealants, fixings, flashings, fire stopping, cavity closers. Individually small, collectively they add up to thousands on any project.

Optimistic labour rates — your best bricklayer on his best day does 60m² of blockwork. Your average across the job will be 40m². Price for average, not best case.

No contingency — things go wrong on every build. Allow 5–10% contingency for the things you can't predict — bad ground, hidden services, weather delays.