Lump-sum price vs unit price in a construction contract: which is better?

Construction contracts use two basic pricing models: lump-sum pricing and unit pricing. A unit-price contract is billed according to the quantities actually completed; a lump-sum contract sets a fixed price for a defined scope. Which model suits you better depends on the project.

Key points at a glance

• Lump sum: budget certainty with a clearly defined scope — but every change immediately leads to variations
• Unit price: transparency and fairness when quantities change — final price only known after site measurement (§ 2 Abs. 3 VOB/B: ±10 % without price adjustment)
• BSB and VPB generally recommend lump-sum pricing for private project owners, provided the work can be fully specified
• A lump sum protects you only as well as the specification behind it — incomplete descriptions undermine the fixed price

What is a unit-price contract?

In a unit-price contract (also: unit-price contract under VOB), individual work items are priced at fixed rates per unit of quantity. Billing is based on the quantities actually completed. The principle is simple: the contractor quotes a price per square metre, linear metre or item. At the end, what was actually installed or carried out is measured and billed accordingly.

The legal basis is found in BGB law on contracts for work (§§ 631 ff. BGB) and, where agreed, in VOB/B § 2 Abs. 2. VOB/B explicitly provides that remuneration under unit-price contracts is calculated using the contractual unit prices and the work actually completed.¹ According to the German Construction Contract Procedures Committee (DVA), the unit-price contract is the most commonly used form in public construction.³

How does billing work?

An example: the quote lists 120 square metres of painting at 12 euros per square metre. If site measurement shows that only 105 square metres were actually painted, you pay for only 105 square metres. Conversely, if it is 135 square metres, the price rises accordingly. Unit prices stay the same; quantities are adjusted.

Advantages of a unit-price contract

• Fair billing: You pay only for what was actually done. No hidden mark-ups on estimated quantities.
• Transparency: Every item is broken down by quantity, unit and price. You can see exactly what accounts for each share of the total cost.
• Flexibility when quantities change: If more or less material turns out to be needed during construction, billing adjusts automatically.
• Comparability: Unit prices are easy to compare between providers because the reference unit is the same. The consumer advice centre therefore generally recommends insisting on unit prices when obtaining several quotes, to create an objective basis for comparison.⁴

Disadvantages of a unit-price contract

• No cost certainty: The final price is only known after work is complete. This makes budgeting harder, particularly on complex projects. According to the Building Owners' Protection Association (BSB), final invoices under unit-price contracts exceed the original quoted total by an average of 8 to 12 per cent.⁵
• Measurement disputes: At handover, disagreements can arise over the quantities actually completed. This costs time and causes stress.
• Quantity risk rests with the project owner: If quantities exceed the estimate, the invoice rises too. The client bears this risk.

What is a lump-sum contract?

In a lump-sum contract, the client and contractor agree a fixed total price for a clearly defined scope. Regardless of how much material is actually installed or how long the work takes, the price remains the same. The contractor bears the quantity risk.

Legally, the lump-sum contract is based on § 631 BGB (contract for work) and, where agreed, on VOB/B § 2 Abs. 7. VOB/B makes clear that remuneration under a lump-sum contract remains unchanged even if the work performed differs from the contractually agreed work, as long as the deviation does not exceed “10 % of the stated quantities”.¹

Advantages of a lump-sum contract

• Cost certainty: The price is fixed from the outset. You know exactly what you will pay as long as the scope remains the same.
• Simple billing: No site measurement, no quantity calculation. The invoice matches the contract price.
• Budget planning: A fixed price is particularly helpful for financing and funding applications (KfW, BAFA), because banks need a binding basis for calculations.⁶

Disadvantages of a lump-sum contract

• Risk from an incomplete specification: If the specification has gaps, the contractor can argue that certain work is outside the lump sum. This leads to variations.²
• Costing allowance: Contractors generally include a risk premium in lump-sum contracts because they bear the quantity risk. The lump sum can therefore exceed the total of the unit prices.
• Limited flexibility: Changes requested during construction almost always lead to variation claims because they alter the agreed scope.
• No refund for lower quantities: If less material is needed than allowed for, you do not benefit. The contractor keeps the full lump sum.

Comparison table: lump-sum price vs unit price

The following table compares the two pricing models against the most important criteria:

When should you choose each pricing model?

The choice between unit and lump-sum pricing depends mainly on the project type and the quality of the specification. Here is a guide by project type:

New build

For a new build with an architect and detailed planning, a lump-sum contract is often the better choice. The scope can be clearly defined beforehand, and quantities are known from the plans. A lump sum's cost certainty is a clear advantage here, particularly where financing is involved. According to the Association of Private Builders (VPB), around 75 per cent of all turnkey new builds use lump-sum contracts.²

Requirement: the specification must be complete and unambiguous. The more detailed the building specification, the less scope for variations. More on contract drafting is available in our construction contract guide.

Renovation

For renovations, particularly existing buildings, much favours a unit-price contract. The reason: surprises in existing buildings often only emerge during the work. Old pipes that need replacing. Mould behind cladding. Structural elements needing remedial work. These uncertainties cannot be priced precisely in advance. The Chamber of Skilled Crafts (HWK) therefore generally recommends unit-price contracts for existing-building renovations, because the actual work required only becomes apparent during execution.⁷

A unit-price contract handles this uncertainty fairly: what actually arises is billed. No more, no less. With a lump-sum renovation, the contractor would offset the uncertainty through a higher risk premium, or disputes over scope would arise later.

Older and listed buildings

For older buildings (pre-1960) and listed buildings, a unit-price contract almost always makes more sense. Uncertainties are particularly great here: asbestos contamination, outdated electrics, floor structures visible only after opening up. In these cases, a lump sum would either be priced too high (to the project owner's disadvantage) or too low (to the contractor's disadvantage, leading to later recovery through variations).

Typical traps in lump-sum contracts

A lump-sum contract sounds secure. But that security has limits, usually in the specification. The most common traps:

Incomplete specification

By far the most common point of dispute in lump-sum contracts. If the specification does not include all necessary work, the contractor can submit a variation for everything missing. And lump-sum contracts often omit more than you think.

Typical gaps: disposal of old materials, scaffolding, site setup, priming, waterproofing, perimeter junctions. These items are often “forgotten” because doing so makes the lump sum appear cheaper.² An apparently cheap lump sum can ultimately cost more than an honest unit-price contract.

Read how to identify and avoid variations in our guide to additional charges.

Hidden variations through vague wording

Phrases such as “painting as needed” or “electrical installation as required” in a specification drive variations. Exactly what “as needed” means is open to interpretation, and in a dispute that interpretation rarely favours the project owner.

Make sure every item in the lump-sum contract is described specifically: areas in square metres, material descriptions, quality standards, number of coats, waterproofing type. The more specific, the less room for additional demands.

“Lump sum based on actual work”

This wording contradicts itself but does occur in practice. A lump sum is, by definition, a fixed price. If the contract says individual services are billed “based on actual work”, it is not a true lump-sum contract. Check carefully whether the fixed-price principle really applies to every item.

Typical traps in unit pricing

Unit-price contracts have pitfalls too. The biggest risks concern quantity calculations and items added later.

Upward quantity deviations

The quote is based on estimated quantities (the stated quantities). If actual quantities are higher, the invoice rises. This is inherent in unit-price contracts, but still frustrating if the estimate was far off.

Tip: have someone familiar with the project check the quoted quantities. Architects or designers can compare them with the plans. This avoids unpleasant surprises in the final invoice. Our guide explains what to look for when comparing quotes: guide to comparing quotes.

Items added later

With unit-price contracts, additional items absent from the quote are sometimes “discovered” during construction. A contractor who finds a wall needs filling before painting will bill this as an additional item if filling is missing from the bill of quantities.

This is fair in principle, provided the additional work is genuinely necessary. Problems arise when items are deliberately omitted to depress the quoted price, then submitted as variations with inflated unit rates. You can recognise this practice because the variation prices significantly exceed the unit prices in the original quote.

Missing or disputed site measurement

Billing by unit prices requires site measurement: jointly establishing the quantities actually completed. If this is not carried out jointly or the measuring methods are unclear, conflicts arise. Insist on site measurement in your presence or your site manager's, with a written record.

Provider comparison: professional review

Whether unit-priced or lump-sum, a building quote should be reviewed before signing. Completeness of the specification is crucial for lump-sum contracts, while plausible quantities and prices matter for unit-price contracts. A professional review helps in both cases. The following table shows common providers:

Cleverbauen24 also offers a free Quickcheck, providing an initial assessment of your quote within a few minutes. Learn more in our guide to quote reviews.

Frequently asked questions

What is the difference between a lump-sum price and a unit price?

Unit pricing is billed according to the quantities actually completed: price per unit multiplied by measured quantity. With a lump sum, the client and contractor agree a fixed price for a defined overall scope, regardless of actual quantities. Unit pricing offers transparency; lump-sum pricing offers cost certainty.

Can a lump-sum price be increased afterwards?

Generally not, as long as the scope stays the same. If the work changes (due to the project owner's requests or unforeseen circumstances), the contractor may submit a variation. Under VOB/B § 2 Abs. 7 Nr. 1, an adjustment may be requested if the quantity change exceeds 10 %. For BGB contracts, § 650c governs remuneration adjustments for changes in scope.

Which pricing model is cheaper?

There is no general answer. For projects that can be priced precisely (new builds with detailed planning), a unit-price contract may be cheaper because no risk premium is included. With uncertain quantities, the lump sum may be cheaper if the contractor overestimates them. In practice, lump sums are often 5 to 15 % above the total of unit prices because contractors protect themselves against quantity risk. The Central Association of the German Construction Industry (ZDB) confirms that trade companies include calculated risk premiums of 5 to 20 per cent in lump-sum contracts, depending on project type and planning detail.⁸

Can I combine both pricing models in one contract?

Yes, this is possible and quite common in practice. For example: structural shell work at a lump sum (because it is predictable), electrical and plumbing installation at unit prices (because exact quantities are only known after strip-out). The contract must clearly state which items are billed as lump sums and which by site measurement.

What happens with increased quantities in a unit-price contract?

For BGB contracts, additional quantities are billed at the agreed unit prices. VOB/B contracts have a special rule (§ 2 Abs. 3 Nr. 2): if the actual quantity exceeds the stated quantity by more than 10 %, either party may request a unit price adjustment. This is intended to prevent the contractor having to work at the same (possibly tightly calculated) price despite a massive quantity increase.

Sources

1. §§ 631 ff. BGB — law on contracts for work (German Civil Code); VOB/B § 2 — remuneration
2. Association of Private Builders (VPB) — Building A to Z guide: lump-sum contracts and typical risks for project owners
3. German Construction Contract Procedures Committee (DVA) — VOB construction procurement and contract procedures
4. Consumer advice centre — commissioning contractors: comparing quotes and assessing prices
5. Building Owners' Protection Association (BSB) — guide to construction contracts and billing models
6. KfW — Federal Funding for Efficient Buildings: requirements for cost estimates and proof of financing
7. Chamber of Skilled Crafts (HWK) — recommendations on contract drafting for renovation and existing-building work
8. Central Association of the German Construction Industry (ZDB) — business principles of quote costing in the skilled trades