Unit price vs lump sum bidding
In a lump sum bid you give one price for a defined scope and carry the quantity risk. In a unit price bid you price each unit of work and get paid for the quantities actually installed, so the owner carries most of the quantity risk. Unit pricing fits work where quantities cannot be known in advance, such as excavation, paving, and utilities.
The difference comes down to who owns the quantities. In a lump sum contract, the contractor quotes one fixed price for the whole scope. If the takeoff was short, the contractor eats it. In a unit price contract, the bid lists items with estimated quantities and a price per unit (per cubic yard, per linear foot, per ton), and payment is based on measured quantities actually installed. If the owner's estimate was short, the owner pays for the extra units. Lump sum suits buildings with complete drawings. Unit price suits horizontal and site work where nobody knows exactly how much rock, unsuitable soil, or patching the job will need.
How each method works
| Feature | Lump sum | Unit price |
|---|---|---|
| What you bid | One price for the defined scope | Price per unit for each bid item |
| Quantity risk | Contractor | Mostly owner |
| Who does the takeoff | Each bidder | Owner provides estimated quantities |
| Payment | Percent complete against a schedule of values | Measured quantities x unit prices |
| Typical work | Buildings, renovations, defined trade packages | Earthwork, paving, utilities, road work, repair contracts |
| Owner's cost certainty at bid | High, unless changes occur | Lower, final cost depends on actual quantities |
| Field paperwork | Lighter | Heavier, quantities must be measured and agreed |
Lump sum progress billing usually runs off a schedule of values. Unit price billing runs off quantity measurements, often signed off by an inspector or the owner's representative each pay period.
When each method fits
Federal rules lay out the logic well. FAR 36.207 says firm-fixed-price contracts are generally used for construction and that lump-sum pricing is used in preference to unit pricing, except when large quantities of work such as grading, paving, building outside utilities, or site preparation are involved; when quantities like excavation cannot be estimated with enough confidence to permit a lump-sum offer without a substantial contingency; when estimated quantities may change significantly during construction; or when bidders would have to expend unusual effort to develop adequate estimates. Many state and local agencies follow similar thinking, which is why road and utility work is so often bid by unit price.
Hybrids are common. A building bid may be lump sum with a few unit prices for rock excavation, unsuitable soil removal, or extra piling. Those unit prices only kick in if the condition is found, and they replace what would otherwise be a change order negotiation.
How to price a unit price bid
- Check the owner's quantities. Do your own takeoff on the major items. Where your number differs a lot from the owner's, think about what that means for your revenue.
- Separate fixed costs from variable costs. Mobilization, traffic control setup, and supervision do not scale with units. If there is a mobilization bid item, put those costs there (within any cap the solicitation sets). If not, spread them across items carefully.
- Price each item at its real unit cost plus markup, using your production rates and crew costs.
- Consider quantity swings. If an item is likely to come in well under the estimate, fixed costs buried in its unit price will not be recovered.
- Read the variation clause. Federal contracts that use estimated quantities may include the variation in estimated quantity clause, FAR 52.211-18, which allows either party to demand an equitable adjustment when an item's actual quantity varies more than 15 percent above or below the estimate, based on cost changes due solely to the variation beyond 115 or 85 percent. State and local contracts often have their own versions. Know which applies before you price.
Worked example: a sewer replacement
Say a utility contractor bids a city sewer replacement with three main items. All prices and quantities are illustrative.
| Item | Est. qty | Unit price | Bid extension | Actual qty | Paid |
|---|---|---|---|---|---|
| 8-inch PVC sewer main (LF) | 2,400 | $118 | $283,200 | 2,380 | $280,840 |
| Rock excavation (CY) | 300 | $145 | $43,500 | 720 | $104,400 |
| Pavement patch (SY) | 1,600 | $62 | $99,200 | 1,550 | $96,100 |
| Total | $425,900 | $481,340 |
Rock came in at 240 percent of the estimate. On a unit price contract, the contractor is paid for every measured yard, about $60,900 more than the bid extension, without a claim. (Under a variation clause like FAR 52.211-18, either side could also ask to adjust the unit price for the quantity beyond 115 percent.) Had the same job been bid lump sum with 300 cubic yards of rock assumed, the contractor would have absorbed 420 extra yards unless the contract had a differing site conditions remedy and the facts supported it. See how to handle differing site conditions claims.
Lump sum: how to manage the quantity risk
- Do a careful quantity takeoff and have someone else check the biggest items.
- Carry contingency for scope that cannot be measured, and state assumptions in your clarifications.
- Ask for unit prices for unknown conditions (rock, bad soil, hidden damage) to be part of the contract.
- Do not front-load the schedule of values beyond what the owner will accept; it invites scrutiny of every pay application.
Choosing a method on private work
On private jobs the contractor often gets a say. A few questions settle it quickly:
- Are the drawings complete? Full construction documents support a lump sum. Schematic drawings or unknown existing conditions push toward unit prices or a cost-plus approach.
- Can quantities be measured cleanly in the field? Unit pricing only works if both sides can agree on what was installed.
- What does the owner value? A lender-funded owner usually wants a fixed number. A facility owner with recurring repair work may prefer unit prices it can reuse across many small jobs.
- How much risk can you carry? A small contractor with thin cash should be careful about lump sum bids on work with big unknowns.
When in doubt, offer the lump sum with a short list of unit prices for the unknowns. Owners get price certainty on the defined scope, and you avoid betting the job on a guess.
Mistakes to avoid
- Trusting the owner's quantities without checking. Your profit depends on the real quantities, so know them.
- Unbalanced bids. Loading prices onto items you expect to overrun and starving others can get a public bid rejected (under FAR 14.404-2, a federal bid may be rejected if line item prices are materially unbalanced), and it damages trust.
- Burying fixed costs in an item that might shrink. If that item underruns, those costs disappear.
- Weak measurement records. On unit price work, unmeasured quantities are unpaid quantities. Record and sign off quantities daily.
- Assuming lump sum means no changes. Owner changes still go through change orders. The change order guide covers the process.
Smart Business Automator tracks quantities, change orders, and billing by job, so unit price pay requests and lump sum schedules of values both come from the same record. See construction accounts receivable automation.
Frequently asked questions
Which is riskier for the contractor, unit price or lump sum?
Lump sum puts quantity risk on the contractor. Unit price shifts most quantity risk to the owner, though the contractor still carries productivity and unit cost risk.
Why do owners use unit price contracts?
When quantities cannot be known in advance, unit prices avoid paying for large bidder contingencies and avoid change order fights over quantity. The owner pays for what is actually installed.
What is an unbalanced bid?
A unit price bid where some items are priced well above cost and others well below, often to gain from expected quantity changes or get paid early. Public agencies can reject bids that are materially unbalanced.
Can a lump sum contract include unit prices?
Yes. Many lump sum contracts include unit prices for specific unknowns such as rock excavation or extra piling, used only if that condition is encountered.
