To read a grading plan, start with the legend and the contour interval, then separate existing grade (usually thin dashed contours) from proposed grade (usually heavier solid contours). Spot elevations give exact heights at key points like finished floor, curb and wall tops. Slope arrows show which way water runs and how steep. Read those four things together and you know where the ground gets cut, where it gets filled, and how water leaves the site.
This guide covers lot grading plans for houses and site grading plans for commercial work. The symbols are the same. Commercial sheets are just denser.
What a grading plan is for
A grading plan tells the contractor what the ground should look like when the job is done and how water will drain. It shows:
- Existing grade: the ground as surveyed before work starts.
- Proposed grade: the finished ground the engineer designed.
- Spot elevations: exact heights where contours aren't precise enough.
- Drainage: slope arrows, swales, inlets, pipes, flow lines.
- Limits: limits of disturbance, property lines, setbacks, retaining walls.
For estimating, the grading plan is the source for cut and fill, topsoil stripping, erosion control lengths and fine grading area. For the general layout of the sheet set around it, see Site Plans 101.
Step 1: Read the legend, notes and benchmark first
Before the linework, read:
- The legend. It tells you which line type is existing and which is proposed on this plan. Dashed existing and solid proposed is the convention, but not a law.
- The contour interval. Often stated in a note ("contour interval = 1 ft"). If not, read two labeled contours and count the lines between them.
- The benchmark and datum. Elevations are relative to a benchmark (BM) on the survey. Check that the grading plan and the architectural finished floor use the same datum. A plan that says FF 5,412.50 and an architectural set that says FF 100'-0" are describing the same floor two different ways.
- General grading notes. Minimum slopes, compaction requirements, topsoil depth, and references to the geotech report usually live here.
Step 2: Read the contours
A contour is a line connecting points of equal elevation. Walk along one and you neither climb nor descend.
Existing contours are usually thin and dashed, labeled with their elevation every few lines (the labeled ones are often heavier "index" contours).
Proposed contours are usually heavier and solid. Where proposed matches existing, the proposed line ties back into the dashed line. That tie-in point is often labeled "ME" (match existing) or "daylight."
Rules that help you read them fast:
- Close together = steep. Far apart = flat.
- Contours point uphill in a valley or swale (the V of the contour points toward higher ground) and point downhill on a ridge.
- Contours never cross, except at a vertical or overhanging feature like a retaining wall, where they stack or appear to merge.
- Where proposed is higher than existing, that is fill. Where proposed is lower, that is cut. Find a spot where a solid line crosses a dashed line: that is a point of zero cut and fill.
Reading an elevation between contours
Most points you care about fall between lines. Interpolate.
Example: A point sits between the 102 and 103 existing contours. Measured on the sheet, it is 6 ft from the 102 line and 14 ft from the 103 line (20 ft total between them). Elevation = 102 + (6 ÷ 20) × 1 = 102.3.
This is the same step you do at every grid node when you calculate earthwork by hand. Our cut and fill from contour lines post works a full example.
Step 3: Read the spot elevations
Spot elevations are exact heights at specific points, usually shown as a small cross, dot or arrow with a number and an abbreviation. They win over contours when the two disagree, because contours are interpolated and spots are designed.
Common places for spots: building corners, finished floor, door thresholds, curb returns, high and low points, inlet rims, pipe inverts, tops and bottoms of walls, and grade breaks.
Grading plan abbreviations
| Abbreviation | Meaning | What it tells you |
|---|---|---|
| FF / FFE | Finished floor (elevation) | Top of the slab or floor at the main level |
| TOF / TF | Top of foundation | Top of the foundation wall |
| FG | Finished grade | Final ground surface, usually top of topsoil or landscape |
| EG / EX | Existing grade | Ground before work |
| TC | Top of curb | Elevation at the top back of the curb |
| BC | Bottom of curb | Elevation at the gutter or flow line side of the curb |
| FL | Flow line | Lowest line water follows in a gutter, swale or channel |
| TW | Top of wall | Top of a retaining wall |
| BW | Bottom of wall | Finished grade at the base of the wall (not the footing) |
| TP / TA | Top of pavement / top of asphalt | Finished pavement surface |
| HP | High point | Water flows away in all directions |
| LP | Low point | Water collects here, usually an inlet |
| GB | Grade break | Slope changes here |
| ME | Match existing | Proposed ties into existing grade |
| INV | Invert | Inside bottom of a pipe |
| RIM | Rim | Top of an inlet grate or manhole lid |
| BM | Benchmark | Reference point for all elevations |
| LOD | Limit of disturbance | Edge of the area you are allowed to work |
Abbreviations vary by engineer. When in doubt, the legend wins.
Step 4: Read slope arrows and do the slope math
Slope arrows point downhill, the way water flows. Most are labeled with a percent, like "2.0%". Some show a ratio instead, like "3:1", which on civil plans means 3 horizontal to 1 vertical.
Slope (%) = rise ÷ run × 100
Ratios and percents convert like this:
| Ratio (H:V) | Percent | Typical use |
|---|---|---|
| 2:1 | 50% | Steep embankment, often the max for mowed or unreinforced slopes per local code |
| 3:1 | 33.3% | Common max for mowable slopes |
| 4:1 | 25% | Gentle embankment |
| 20:1 | 5% | Ground falling away from a house |
| 50:1 | 2% | Paved areas, swale bottoms |
| 100:1 | 1% | Very flat; drainage gets marginal |
Example: checking a lot's drainage
A house plan shows FF 105.50 and a spot grade at the foundation of 104.75 (9 inches below FF). Ten feet out, a spot reads 104.25. Then a side-yard swale runs 72 feet to a spot of 102.80 at the street.
- Fall away from the foundation: 104.75 − 104.25 = 0.50 ft over 10 ft = 5.0%. That meets the International Residential Code's R401.3 requirement of at least 6 inches of fall in the first 10 feet. Check your local amendments.
- Swale slope: 104.25 − 102.80 = 1.45 ft over 72 ft = 2.0%.
- Floor above grade: FF 105.50 minus foundation grade 104.75 = 0.75 ft, so the finished floor sits 9 inches above the adjacent ground.
If you measured the swale at 72 ft but the spots only dropped 0.30 ft, that is 0.4%, flat enough to pond. That is worth an RFI before anyone grades it.
Example: finding slope from contours
Two proposed 1-ft contours are 40 ft apart, measured at a right angle to the lines. Slope = 1 ÷ 40 = 2.5%. If they are 8 ft apart, slope = 1 ÷ 8 = 12.5%. Measure perpendicular to the contours. Measuring at an angle makes slopes look flatter than they are.
Step 5: Find the swales, pads and drainage path
Swales
A swale shows up as contours forming a V or U that points uphill, usually with a flow line and slope arrows down its center. Residential swales commonly run at 1% to 2% or steeper. Note any lining callout (sod, riprap, erosion mat), because that is a separate line item.
Pads
A building pad is a flat area graded for a foundation. On commercial plans the pad elevation may be called out directly. On lot plans you often only get the finished floor. The pad itself sits below FF by the slab and base thickness, and that difference changes your cut and fill. Our AI cut and fill post shows how much a missed subgrade adjustment can move the number.
Drainage structures
Follow the water: slope arrows lead to swales or gutters, which lead to inlets (labeled with RIM elevations), which lead to pipes (labeled with INV elevations, size and slope). Check that inverts drop in the direction of flow. Pipe slope = (upstream INV − downstream INV) ÷ pipe length.
A grading plan reading checklist
- Legend read: which linetype is existing, which is proposed.
- Contour interval confirmed for each set.
- Benchmark and datum match the architectural FF.
- Every spot elevation near the building checked for positive drainage.
- Swale slopes calculated from spots, not eyeballed.
- Retaining walls noted, with TW and BW.
- Limits of disturbance and silt fence lines measured.
- Grading notes and geotech references read for topsoil depth and compaction.
From reading to quantities
Once you can read the plan, the quantities come from it: cut and fill from the two sets of contours, stripping and fine grading by area, silt fence and swale lining by length. In Foreman AI you can ask questions about the grading sheet in plain English ("what's the finished floor and where's the low point?") and get answers that cite the sheet, then run the earthwork takeoff on the same PDF to get cut, fill, net, a heat map and a report. Upload a plan set and try it free.
FAQ
How do you read elevations on a grading plan?
Elevations appear two ways: contour lines, each labeled or countable from a labeled index contour, and spot elevations at specific points. For a point between contours, interpolate by its distance between the two lines. Spot elevations take priority over contours when they conflict.
What is the difference between dashed and solid lines on a grading plan?
By convention, dashed lines are existing contours and solid lines are proposed contours. Always confirm with the plan's legend, since some engineers use different line weights or colors.
What do TW and BW mean on a grading plan?
TW is top of wall and BW is bottom of wall, usually a retaining wall. BW is the finished grade at the base of the wall, not the bottom of the footing. The difference between them is the exposed wall height.
How do you calculate slope from a grading plan?
Divide the change in elevation by the horizontal distance and multiply by 100. Between two spots 50 ft apart with elevations 101.00 and 100.00, the slope is 1 ÷ 50 = 2%. Between contours, measure the distance at a right angle to the lines.