Survey & Layout Field Guide — Stations, Grade, Slope & Crossfall

1Stationing & offsets

Stations are the mile markers of a job — every point on the alignment has one.

A station like 10+250 means 10,250 metres along the alignment from the start. The offset is how far left or right of the centreline you are — RT for the right side, LT for the left, looking in the direction of increasing station (or as defined on the plans). So "16+905 LT 1.8" is a point 1.8 m left of centreline at station 16+905 — exactly how field QC samples and cores are located.

Every point on the job is a station + side + offset — the same language QC cores use.

2Grade & slope

Percent grade is rise over run — and it tells you the fall over any distance.

Grade (%) = Rise (m) ÷ Run (m) × 100 · Fall = Length × Grade %

The question everyone asks: "2% over 12 metres?"

Fall = 12 m × 0.02 = 0.24 m = 240 mm

Rise over run — grade % scales the fall with the length.

CalculateSlope / grade calculatorRise over run, percent grade and fall over a distance. RelatedCut & fill calculatorTurn grades into excavation volumes.

3Crossfall & crown

The road isn't flat — it sheds water off the crown to the edges.

Crown in the middle, crossfall to each edge — typically around 2% on paved roads.

Crown is the high point in the middle of the road; crossfall is the slope from the crown to each edge, usually about 2% on pavement. It exists to drain water off quickly. On a superelevated curve, the "crown" is replaced by a one-way slope into the curve. When you're setting grade or checking a mat, the crossfall is part of the layout — a flat spot where water ponds is a problem even if the spot is "level."

Field tipCrossfall is checked with a slope or grade tool at the finished surface. On asphalt days, check it right behind the roller — fixing crossfall after the mat sets means grinding.

4Elevation & vertical

Elevation differences are cut or fill — and they're the start of every earthwork quantity.

An elevation difference between the existing ground and the design grade at a point tells you whether it's cut (take material out) or fill (bring material in). Multiply the difference by the area it applies to and you have volume — which is exactly what the cut & fill calculator does. Elevations also drive drainage: minimum falls for pipes, ditches and subgrade are all set by elevation differences over distance (same grade math as above, just vertical).

CalculateCut & fill calculatorBalance excavation volumes across a site. RelatedEarthworks field guideVolumes, compaction and excavation in one place.

5Conversions

The same slope, three different ways of saying it.

mm/m to %: 10 mm per metre = 1% (because 10 mm ÷ 1000 mm = 1%). So 20 mm/m = 2%, 25 mm/m = 2.5%.
Percent to ratio: 2% = 1 in 50 (100 ÷ 2). 4% = 1 in 25. Common drainage slopes like 1:50 or 1:100 are just percentages written differently.
Percent to degrees: degrees = arctan(grade) — 2% ≈ 1.15°, 5% ≈ 2.86°, 10% ≈ 5.71°. Most field layout works in percent, not degrees.

1% = 10 mm per metre = 1 in 100

ConvertSlope / grade calculatorPercent, ratio, mm/m and fall in one tool. ConvertUnit converterLength, area, volume, mass — metric and imperial.

6Field tips

The stuff you learn walking the grade stakes.

Field tip — stationsAlways confirm which side of the centreline "left" and "right" are measured from on your job — some plans use the direction of increasing station, some use the direction of travel. A flipped sign is a 7 m mistake.

Field tip — slopePercent grade scales with distance — a 2% slope is 20 mm of fall per metre. Do the fall math in your head before you set anything: it catches most errors fast.

Field tip — recordsWrite station + offset + elevation on every record, the same way you'd expect to find it. You'll thank yourself when something gets questioned at the end of the job.

Put this guide to work.

Run the grade and slope numbers with the calculator, then carry the layout into the earthwork workflow.

Open the slope calculator →

Survey & layout, explained for the field.