Cut and Fill Explained
Cut and fill is the core quantity in earthworks. It sounds simple — how much earth to move — but the number depends entirely on what you compare against. This guide explains how cut/fill is calculated and where it commonly goes wrong.
What cut and fill means
Cut is the volume of material you must remove to reach a target surface; fill is the volume you must add. Together they describe the earthwork needed to turn the existing ground into the design surface.
The result is usually reported as separate cut and fill volumes, and sometimes as a net balance, because a site that balances cut against fill moves less material off-site.
The reference surface is everything
The same terrain can give very different cut/fill numbers depending on the reference. Common references are the real existing terrain, a flat design level, or another design surface.
This is why good software lets you choose the reference explicitly. If the reference is ambiguous, the volume is ambiguous.
Comparing two surveys
A related use of cut/fill is comparing two surveys of the same site taken at different times. The difference tells you how much material was added or removed between them — useful for progress tracking and reconciliation.
Common pitfalls
Watch for mismatched extents (the two surfaces must overlap), the wrong reference, and using a surface model where a bare-earth model was needed. Computing directly on a clean DEM, with an explicit reference, avoids most of these.
Compute cut and fill in STREAM
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