What do contour lines on a grading plan mean?

Contour lines connect points on the ground that share the same elevation. Lines that are close together represent steep slopes; lines that are far apart represent gentle ground. On most grading plans, existing contours are shown as thin or dashed lines, and proposed contours are shown as bold or solid lines, so the difference between the two shows what fill or cut is required.

What is a spot elevation?

A spot elevation is the exact elevation at a specific point on the site, written next to the point on the plan, such as 1042.50. Spot elevations are used at building corners, parking-lot corners, drain inlets, and any place where the contour interval isn't precise enough.

How do I tell which way water flows on a grading plan?

Water flows from higher elevations to lower elevations, perpendicular to the contour lines. Most grading plans also show small drainage arrows that mark surface flow direction, plus storm-drain inlets and outlet structures. To trace runoff, follow the slope arrows, look for low points, and identify where flow leaves the site or enters a storm-drain.

What is the minimum slope for surface drainage?

Industry standards generally require a minimum 1% slope on paved surfaces and 2% slope on landscaped surfaces to ensure positive drainage. Some jurisdictions accept slightly less, especially on accessible routes that are limited to 2% cross slope. Slopes less than 1% on pavement risk ponding and long-term drainage problems.

Why does my grading plan show cut and fill volumes?

Cut and fill volumes show how much earth must be excavated (cut) and added (fill) to reach the proposed grades. The volumes drive the earthwork cost and indicate whether the site can be balanced (no soil imported or exported) or if the project will need to truck dirt in or out, which is a significant cost item.

How to Read a Grading Plan

A grading plan shows existing and proposed ground elevations across a site, using contour lines to represent constant elevations, spot elevations to mark exact heights at specific points, and slope arrows or drainage callouts to show how water moves. Reading one is mostly a matter of learning a small vocabulary of symbols, then walking the site mentally, low to high, to confirm everything drains the way the engineer intended.

You do not need an engineering background to read a grading plan well enough to ask the right questions. Most of the issues that bite a project later (water against the building, parking-lot ponding, cut/fill way over budget) are visible on the plan if you know what to look for. This guide walks through the symbols, the workflow for reviewing a sheet, and a checklist of red flags. If you want the broader context for what a grading plan is and why it matters, start with our companion piece on what a grading plan is, then come back here for the read-along.

The five things every grading plan shows

Civil sets vary in style, but every grading plan shows the same five elements:

Existing contours. Usually thin, dashed, or screened-back lines representing the current ground.
Proposed contours. Bolder, solid lines representing the finished ground after grading.
Spot elevations. Numbers placed at specific points (building corners, parking-lot corners, top and bottom of curbs, drain inlets) representing the exact finished elevation at that point.
Drainage symbols. Arrows showing surface flow direction, storm-drain inlets, swales, ridge lines, and outlet structures.
Reference data. A north arrow, a graphic scale, a benchmark or datum reference, the plan title, the engineer's stamp, the revision history, and a sheet index.

Contour lines: the most important symbol on the sheet

A contour line is a single elevation drawn across the ground. Stand on a contour line and you do not change elevation as you walk along it. Step off the line uphill or downhill, and you change by the contour interval.

Two contour properties to read:

Contour interval. The vertical spacing between adjacent contours, called out in the legend (typically 1 ft, 2 ft, or 5 ft on land development projects). A 1 ft interval is high resolution and good for detailed grading; a 5 ft interval is for large-scale or steep terrain where 1 ft would be unreadable.
Contour spacing. The horizontal distance between adjacent contours on the plan. Lines close together = steep slope. Lines spread out = gentle slope. This is the visual cue that lets you read steepness at a glance.

To estimate slope from contours, divide the contour interval (vertical) by the distance between contours measured at the plan scale (horizontal). A 2 ft interval with contours 20 feet apart is 2/20, or 10% slope.

Existing vs proposed: where the work is

Almost every grading-plan review starts by comparing existing and proposed contours. The differences tell you where the project is cutting earth, where it is filling, and how much.

Where proposed contours bulge outward (downhill) from existing, the project is filling at that spot.
Where proposed contours pull inward (uphill) from existing, the project is cutting at that spot.
Where they overlay, the ground is staying as-is.

The areas of the site that show large divergence between existing and proposed contours are where the earthwork dollars are. If a developer is trying to estimate how aggressive the grading is at a glance, this is the test.

Spot elevations: the precision that contours can't give you

Contours show general topography. Spot elevations show specific, controllable points. You will see them at:

Building finished-floor elevations (FFE), typically called out as "FF" or "FFE" with a value
Parking-lot corners and accessible-route landings
Top and bottom of curbs (TC / BC or TOC / BOC) at every transition
Storm-drain inlets, manholes, and outlet structures
High and low points of swales and channels
The face of every retaining wall

Spot elevations are the engineer's way of saying "this exact number, at this exact point, no interpolation." They override contours where they appear, and field crews build to the spot elevations first.

Drainage callouts: how the site moves water

Civil drawings show drainage with a small set of repeated symbols:

Slope arrows. Short arrows on paved or graded surfaces showing the direction of surface flow. Often labeled with a percent slope (e.g., 1.5%).
Storm-drain inlets. Squares, rectangles, or circles representing curb inlets, area drains, or yard drains. Usually labeled with a structure ID (e.g., CB-1) and rim/invert elevations.
Pipe runs. Lines connecting structures, with size, slope, and material called out (e.g., 18" RCP @ 1.0%).
Swales and ridge lines. Long curving lines that mark the bottom of a drainage path or the top of a divide.
Outlet structures. Headwalls, flared end sections, or detention/retention pond outlets where water leaves the site.

The trick when reviewing drainage is to start at the highest point and trace flow downhill, structure by structure, until water leaves the site. Anything that doesn't have a clear path off-site is a low spot, and low spots without inlets are puddles waiting to happen.

A 5-step workflow for reviewing a grading plan

Here's the sequence Paul uses when handed a grading plan to review:

Step 1: Confirm the basics

Before reading content, confirm the orientation: north arrow, scale, sheet number, plan title, engineer's stamp, and revision date. If any of those are wrong or missing, the rest of the review is on shaky ground.

Step 2: Find the building and read finished-floor elevation (FFE)

For a site with buildings, the FFE is the keystone elevation. Everything else is set relative to it. Confirm:

FFE is at least 6 inches above adjacent finished grade for positive drainage away from the building
FFE is above any 100-year floodplain elevation if the site is in a flood hazard area
FFE makes sense relative to the existing ground (not requiring 8 ft of fill on a tight residential site)

Step 3: Trace surface flow, low to high, looking for low spots

Walk the plan visually. Pick a high point on the proposed contours and follow water downhill, slope arrow by slope arrow. Every drop of water on the site should reach either a storm-drain inlet or a controlled site-exit point. Anywhere flow stops, runs back uphill, or pools without an inlet is a problem.

Step 4: Check parking-lot and pavement slopes

Confirm that paved areas are between 1% and 5% slope — enough to drain, not so much that they fail accessibility, parking, or driving comfort. Look at every parking-lot corner: top of curb to bottom of curb to inlet rim should make sense.

Step 5: Sanity-check earthwork

Look at where existing and proposed contours diverge most. If a building pad sits 5+ ft above existing ground, the project is importing fill (expensive). If a building is 5+ ft below existing ground, the project is exporting cut (also expensive, plus the project may have rock or groundwater issues). A balanced site (cut roughly equals fill) is usually the cheapest outcome, and a good grading plan documents the volumes.

Red flags to watch for

The grading-plan issues that cause the most expensive problems on real projects:

FFE too close to adjacent grade. Less than 6 inches between FFE and finished grade leads to water at the building and basement issues.
Negative slope away from a building. Even if the contours look correct, watch for slope arrows pointing toward the foundation.
Low spots without inlets. A patch of contours that closes on itself (like a target) with no drainage symbol means a puddle.
Pavement slopes < 1%. Common in flat-site designs and a frequent source of post-construction ponding.
Retaining-wall heights inconsistent with face elevations. A 6 ft wall on the wall plan should match a 6 ft elevation difference on the grading plan.
Cut or fill volumes not balanced. If the site requires importing or exporting tens of thousands of cubic yards and the budget didn't account for it, that's a major surprise.
Existing-tree protection ignored. Heavy fill within a tree's root zone, or cut that severs roots, kills mature trees the project intended to save.

Where to get a deeper read

Once you can read contours and spot elevations, most of the rest of a grading plan becomes legible. The remaining 10% — calculating storm-pipe capacities, sizing a detention pond, confirming a soil's settlement behavior — is what a civil engineer does. For more on the underlying civil work, see grading and drainage design services or read the stormwater management guide for how grading and stormwater fit together.

If you have a grading plan in front of you and want a second set of eyes before you sign off, that's the kind of review Land Pro Civil does often. Send it over; you'll get a real PE's read, not a generalist.

How to Read a Grading Plan: A Visual Guide for Developers.