What is a construction setout offset?

An offset is a measured distance from a known baseline, usually parallel to the baseline or perpendicular to it, used to locate a construction feature.

Can this calculate the final point coordinates?

Yes. Given a baseline start point and direction angle, the calculator resolves a point using along-line and perpendicular offsets.

Does an offset replace survey control?

No. It is a geometric calculation and should be checked against project control.

Baseline-to-feature layout

Building Setout Offset Calculator

Locate a construction point from a known baseline using an along-line station and a perpendicular offset. The resulting coordinate makes the offset assumption easy to verify.

Baseline and offset

Baseline start X

Baseline start Y

Baseline direction angleDegrees counterclockwise from +X.

Along-line distance

Perpendicular offsetPositive = left of travel direction.

Unit

Enter baseline direction, station and offset.

Setout point

Resulting point——

—Along-line component

—Perpendicular component

—Baseline distance

—Angle

—

Offset geometry

The baseline direction is converted to a unit vector. The station advances along that vector. The offset advances in the perpendicular direction, producing the final point coordinates.

X = X₀ + station × cos(θ) − offset × sin(θ)
Y = Y₀ + station × sin(θ) + offset × cos(θ)

Example

For a baseline heading 30°, a 12 m station and a +3.5 m left offset, the point is displaced along the baseline and then shifted perpendicular to it. This is particularly useful when a wall or footing line is set from a known reference line.

Important sign convention

Changing the sign of the offset moves the point to the opposite side of the baseline. Agree the convention with the project setout method before transferring the value to site.

Frequently Asked Questions

Can the baseline angle be 90°?

Yes.

Can the offset be negative?

Yes. Negative means the opposite side under the stated sign convention.

Can the start point be non-zero?

Yes. Use the project control coordinates.