Yard slope calculator

What the result tells you

Slope describes how much the ground rises or falls over a horizontal run. It is one useful observation when investigating a wet yard. Positive grading beside a building falls away from the wall; negative grading falls toward it. The same percentage can describe either direction, so record which point is higher before entering the values.

A calculated percentage does not tell you how quickly the soil absorbs water, how much roof runoff reaches that spot, whether an outlet is permitted or whether the whole yard follows its approved drainage design. Use it with the backyard drainage observation routine, rather than treating a number as the answer to every puddle.

The formula, with two examples

Slope percentage = elevation difference ÷ horizontal distance × 100. Converting units first matters. Four centimetres of fall over two metres is 0.04 ÷ 2 × 100 = 2%. Six inches of fall over ten feet is 6 ÷ 120 × 100 = 5%. These are mathematical examples, not instructions to build either grade.

Measure horizontal distance rather than following the sloping surface with a tape. Enter the magnitude of the elevation change as zero or a positive number. Use the direction control to explain whether that fall heads toward the house, away from it or across another part of the yard. A zero result means the two endpoints have the same measured elevation; it does not prove every point between them is level.

How to record a small accessible segment

Choose two points on stable ground you can reach safely. Identify the point nearest the house and mark the measurement direction in your notes. A straight board and spirit level can help with a short segment: hold the board horizontal from the higher point, then measure the vertical gap to the ground at the lower end. Measure the horizontal run covered by that same segment.

Do not walk into floodwater, balance across a slippery ditch, open a drain cover or climb onto a roof to collect measurements. Stop if the setup is unstable or you cannot make the board level. Uneven ground, grass thickness and a bowed board can distort the reading. For a long yard, tight clearances, shared routes or construction decisions, professional elevation measurements are more suitable than extrapolating from a short board.

Record the date, weather, endpoints, units, direction and surface. Take an optional photo that shows the setup without revealing people or private details. Repeat along the accessible route only if safe. A low point between your endpoints may still hold water even when the average slope looks favourable.

Use current Calgary guidance for the next decision

The City’s positive lot drainage guidance explains responsibilities and the relationship between site grades and surface routes. Its lot grading tolerance chart distinguishes surfaces and construction contexts. A simple percentage cannot establish the required elevations, setbacks, clearances or municipal approvals for your lot.

Before changing grade, locate the approved plan where available and confirm the route beyond the measured segment. Raising one low spot can send water toward a doorway, fence or neighbouring property. Excavation also requires utility planning and suitable professional advice. Read positive and negative grading explained for the terms, and foundation water pooling guidance when water is near the wall.