DoubtCalc
DoubtCalc

Pergola Shade Calculator

Estimate how much shade your pergola will provide based on rafter dimensions, spacing, orientation, and cover material.

How to use this calculator

Enter your pergola dimensions including the overall length and width in feet. Then specify the rafter size, such as 2x6 or 2x8, and the spacing between rafters in inches. The calculator uses these measurements to determine the percentage of the overhead area blocked by the rafters alone.

Choose your cover material if applicable. Options range from no cover with open rafters only, to shade cloth in various densities, fabric canopies, and solid roofing panels. The calculator combines the rafter shade with the cover material shade to give you total estimated coverage at different sun angles throughout the day.

Understanding pergola shade patterns

Shade from a pergola is not constant. It changes throughout the day as the sun moves across the sky. At midday when the sun is nearly overhead, the shade falls directly below the rafters in narrow bands. In the morning and late afternoon, when the sun is at a lower angle, the shade shifts to one side and the rafter shadows become longer and more overlapping, which actually increases the shaded area on the ground.

The season also matters. In summer, when the sun sits higher in the sky, shade falls closer to the base of the pergola. In winter, the lower sun angle casts shade farther out to the side. This seasonal shift is one reason pergolas are so popular in warmer climates. They block the intense overhead summer sun while allowing the lower winter sun to pass through at an angle and warm the space.

Frequently asked questions

How much shade does a standard pergola provide?
A standard open rafter pergola with no cover material provides roughly 20% to 30% shade at midday. The exact amount depends on rafter width and spacing. Wider rafters spaced closer together block more sun. Adding a shade cloth or canopy cover can increase coverage to 50% or even 90% depending on the material.
Does pergola orientation affect shade?
Yes, orientation has a major impact. Rafters running east to west provide more consistent shade throughout the day because the sun travels roughly south across the sky in the northern hemisphere. Rafters running north to south create moving stripes of shade that shift as the sun moves. For maximum afternoon shade, orient the pergola so the long side faces west.
What shade cloth percentage should I use?
Shade cloth comes in densities from 30% to 90%. A 50% cloth is a good middle ground that blocks about half the sun while still letting air and some light through. For dining areas, 70% to 80% is popular because it provides noticeable cooling without making the space feel dark. For plants underneath, 30% to 50% works well for most sun loving species.
How do rafter spacing and width affect shade coverage?
Wider rafters block more sun. A 2x6 rafter on edge provides about 5.5 inches of shade width, while a 2x8 provides about 7.25 inches. Closer spacing increases shade percentage because more rafter surface covers the opening. Typical rafter spacing is 12 to 16 inches on center, which gives 25% to 35% shade from the rafters alone at midday.

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