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Units of Measureaka: PSIaka: psi

Pound Per Square Inch (PSI)

In Plain English

A pressure measurement most commonly used to specify how strong concrete is.

Definition

Pounds per square inch (PSI) is a unit of pressure or stress measurement equal to one pound-force applied over an area of one square inch. In construction, PSI is used to specify the compressive strength of concrete (e.g., 3,000 PSI, 4,000 PSI, 6,000 PSI), as well as the pressure rating of hydraulic systems, pneumatic tools, grouting operations, and water pressure systems. Concrete PSI requirements are established by the structural engineer based on the member's design loads.

Why It Matters in Bidding

Concrete compressive strength in PSI is one of the most pricing-sensitive specs an estimator reads, because each step up (3,000 to 4,000 to 6,000 PSI) raises the cost per cubic yard and can require admixtures, longer cure times, or added testing. Misreading the specified strength is a common bid error that either inflates a proposal and loses the award or wins work that is bid below cost.

Example

When pricing the foundation package, the estimator caught that the slab-on-grade called for 3,000 PSI but the columns required 5,000 PSI, so the bid carried two separate concrete unit prices instead of one.

Related Terms

Cubic YardYard (concrete)Unit Price

Frequently Asked Questions

Higher-strength mixes cost more per cubic yard because they need more cement, admixtures, and tighter quality control. An estimator must read the structural drawings to match each pour to its specified strength, since pricing every element at the highest PSI inflates the bid and pricing too low erodes the margin once concrete is delivered.
The structural engineer of record sets the required compressive strength based on the design loads each member carries, then documents it in the structural drawings and specifications. Contractors and estimators do not choose the value; they price and supply concrete that meets the stated PSI and the field testing that verifies it on site.
A testing lab casts cylinders from delivered concrete and breaks them, commonly at 7 and 28 days, to confirm the mix reaches its specified strength. Contractors should carry the cost of this testing in their estimate when the specifications assign it to them, since failing breaks can trigger investigation, removal, and rework that no one budgeted.

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