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Calcimator

Pavement Thickness Calculator

Design flexible pavement thickness using a simplified AASHTO 1993 method. Calculates required structural number and layer thicknesses for asphalt, base, and subbase.

Inputs

AASHTO 1993: local road logESAL 5–6; arterial 6–7; interstate/highway 7–8

psi

AASHTO T307/Mr=1500×CBR: soft clay 3,000 psi; stiff clay 8,000 psi; sand/gravel 15,000–20,000 psi

Results

Required Structural Number

3.9

Asphalt Surface

4 in

Total Pavement Thickness

21 in

≈ 6 credit cards

Aggregate Base10 in
Subbase7 in
How to Use This Calculator
  1. Enter design ESALs (log₁₀), desired reliability level, and serviceability loss.
  2. Set resilient modulus and other layer parameters.
  3. Review required pavement thickness (inches) per AASHTO 1993 design guide.

How the result changes with Design ESALs (log₁₀)

Design ESALs (log₁₀)Required Structural NumberAsphalt SurfaceTotal Pavement Thickness
4.52.33 in12 in
5.753.654 in19 in
7.255.97 in30 in
8.58.359 in44 in

What each input means

Design ESALs (log₁₀)
Logarithm (base 10) of total 18-kip equivalent single axle loads over design life per AASHTO 1993 Pavement Design Guide. Log 6 = 1,000,000 ESALs. Local roads: 5–6; arterials: 6–7; interstate: 7–8.
Reliability
Design reliability level. Higher reliability requires thicker pavement. Interstate = 90-99%; local roads = 50-80%.
Serviceability Loss (ΔPSI)
Allowable decrease in Present Serviceability Index. Typical: initial PSI = 4.2, terminal = 2.0-2.5, so ΔPSI = 1.7-2.2.
Subgrade Resilient Modulus
Resilient modulus of the subgrade soil per AASHTO T 307 or AASHTO 1993 correlation from CBR: Mr ≈ 1,500 × CBR. Soft clay ≈ 3,000 psi; stiff clay ≈ 8,000 psi; sand/gravel ≈ 15,000–20,000 psi.
Drainage Coefficient
Modifier for quality of drainage. Excellent drainage = 1.2-1.4; poor drainage = 0.4-0.8; fair = 1.0.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Design ESALs (log₁₀) = 6, Reliability = 90, Serviceability Loss (ΔPSI) = 2, Subgrade Resilient Modulus = 5000 = 5 input(s) provided
  2. Calculate Required Structural Number
    Required Structural Number
    3.9 = 3.9
  3. Calculate Asphalt Surface
    Asphalt Surface
    4 = 4
  4. Calculate Total Pavement Thickness
    Total Pavement Thickness = asphaltThickness + baseThickness + subbaseThickness
    21 = 21
  5. Calculate Aggregate Base
    Aggregate Base
    10 = 10
  6. Calculate Subbase
    Subbase
    7 = 7

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