Construction

Vertical Curve Calculator

Find the K-value of a vertical highway curve.

Incoming grade (G₁) (%)

Outgoing grade (G₂) (%)

Curve length

Calculated Output

K-value (ft/%) 0.2

Algebraic difference (%) 5

Formula: K = L ÷ |G₂ − G₁|

Step-by-Step Breakdown

1. Values used:

2. Incoming grade (G₁) = 3 %

3. Outgoing grade (G₂) = -2 %

4. Curve length = 1

6. K-value = 0.2ft/%

7. Algebraic difference = Incoming grade (G₁) - Outgoing grade (G₂) = 3 - -2 = 5%

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The math behind it

K = curve length ÷ |outgoing grade − incoming grade| (in %). Higher K = gentler curve.

3% to −2% over 500 ft → K 100.

Design speed?

Minimum K increases with design speed — check highway standards for your jurisdiction.