How to Check Driveway Slope With a Level

Set a straight board and a level, or use a smart level, and read rise over run. A quarter inch of drop per foot is about 2 percent. Check the direction water actually runs, including toward the garage. Write the percent down before you pay for grade work.

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How to take the reading

You do not need a survey crew to learn whether a driveway is pitched the wrong way. Set a straight board on the pavement, put a carpenter's level on it, and shim one end until the bubble centers. Measure the shim height and divide by the length of the board. A quarter inch of drop in one foot is about 2 percent. A half inch in one foot is about 4 percent. A smart level that reads percent does the same job if you check it on a surface you already know. Take readings along the drive and across it. Water follows the cross slope as well as the length. A driveway that falls nicely toward the street can still send a sheet of water into the garage if the last ten feet tilt back.

What the number is for

Ordinary driveway drainage and an accessible route do not use the same limit. A slope that sheds water off a car drive can be too steep for a wheelchair stall or an access aisle. If you are building accessible parking, check the current ADA Standards and the local official before you pave. A blog percent is not a legal conclusion. For a normal home drive, the practical test is also simple: water should leave the mat, should not pond in the wheel path, and should not run into the building. Write the percent down before you pay for grade work. A level on a short board will not replace a survey at the street, where curb height and sidewalk cross slope are often controlled by the town.

How slope meets the tonnage

Slope does not change the planning tons by itself. Area and compacted thickness do. Tons equal length in feet times width in feet times inches divided by 12, times 145, divided by 2000. A steeper drive can still use that formula. What slope changes is whether you need extra thickness at an edge, a swale, or a leveled bay, which adds area or depth and therefore tons. Fix the base grade to the slope you measured before the asphalt arrives, because the mat will follow the stone. A thin overlay will not reverse a driveway that pitches into the garage. If the level says the last section falls toward the door, plan to correct the base, not to hide it under sealer.

A practical sequence

Set a straight board and a level, or use a smart level, on the pavement.
Read rise over run and convert a quarter inch per foot to about 2 percent.
Check both the length and the cross slope, including the garage end.
Write the percent down and correct the base before you order asphalt.

The mistake to skip

Checking only the long slope and missing a cross slope into the garage.

Questions people ask

Is 2 percent required on every driveway?

Two percent, about a quarter inch per foot, is a common drainage pitch and a figure cited for accessible stalls. It is not a universal driveway code. A home drive may be steeper and still drain. An accessible stall has its own flatness limit. Check the current ADA Standards and the local official for that work. Confirm water leaves the mat and does not enter the building.

Can I trust a phone level?

A phone can show the direction of slope if you set it on a straight board, not on a single stone. Calibrate it on a surface you have checked with a carpenter's level. Take several readings. One tilted phone photo is not a grade plan. Use the number to decide whether the base needs work before paving, then confirm the street tie-in with whoever controls that grade.

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