Patio Fall
Calculator
Patio Fall Calculator - Calculate Required Slope and Gradient
Getting the correct fall on a patio is essential for drainage, surface performance and long term durability. This Patio Fall Calculator allows you to quickly calculate the required fall in metres and the gradient percentage needed to ensure water runs away from buildings and does not pond on the surface.
Whether you are installing porcelain paving, natural stone, concrete slabs or block paving, accurate patio fall calculation prevents standing water, joint failure and freeze thaw damage. This patio gradient calculator is designed for UK landscaping professionals working in metres and millimetres.
Use this patio slope calculator to:
• Calculate required fall in metres
• Convert fall into gradient percentage
• Determine slope over any patio length
• Ensure compliant drainage away from structures
Correct patio fall is not guesswork. It is a calculated requirement based on length and desired gradient.
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How Much Fall Should a Patio Have?
A typical patio should have a minimum fall of 1 in 80 for standard paving installations. In some cases, 1 in 60 may be specified for improved drainage, particularly with porcelain paving.
This means:
1 in 80 equals 12.5mm fall per metre
1 in 60 equals approximately 16.7mm fall per metre
The longer the patio, the greater the total fall required. This patio fall calculator instantly works out the correct drop based on the surface length.
Patio Gradient Percentage Explained
Gradient percentage is another way of expressing fall.
To calculate gradient percentage:
Fall divided by length multiplied by 100 equals gradient percentage.
For example, a 50mm fall over 4 metres equals a 1.25 percent gradient.
Understanding gradient percentage is particularly useful when setting out levels using laser levels or digital measuring equipment.
Why Correct Patio Slope Matters
Insufficient patio fall can result in:
• Surface water ponding
• Grout deterioration
• Edge staining
• Freeze thaw damage
• Water tracking towards buildings
Excessive fall can create usability issues and uneven seating areas.
A properly calculated patio gradient ensures controlled drainage without compromising surface comfort.
Patio Fall for Porcelain Paving
Porcelain paving requires careful fall calculation due to its very low water absorption rate. Surface water must drain efficiently as it cannot be absorbed into the slab.
Many installers prefer a minimum of 1 in 60 when installing porcelain patios to reduce the risk of standing water.
Using this patio fall calculator ensures accurate level setting before bedding and laying begins.
Frequently Asked Questions
Generally 1 in 80 is considered the minimum for standard paving. For porcelain paving, many installers prefer 1 in 60.
Multiply the patio length by the desired fall ratio. For example, 4 metres at 1 in 80 equals 50mm total fall.
1 in 80 equals 1.25 percent gradient.
1 in 60 equals approximately 1.67 percent gradient.
Yes. Excessive slope can create usability problems and affect furniture placement. It may also look visually incorrect.
In most domestic installations, fall runs away from the building in a single direction. Complex layouts may require cross falls or channel drainage.