How to Estimate Dirtwork: A Step-by-Step Guide for Small Contractors

If you’ve been in the excavation or site prep business for any length of time, you know that dirtwork estimating is where bids are won — and where margins are lost. Underestimate a cut-and-fill job and you’re eating the difference. Overestimate and you lose the contract to someone who did their homework.

The good news: dirtwork estimating is a learnable skill. It follows a consistent process, and once you understand the steps, you can build estimates you’re confident in — job after job.

Here’s how to do it.

Step 1: Get the Right Plans and Specs

Before you touch a number, make sure you have the documents you need:

• Grading plan — shows existing and proposed elevations, cut/fill areas, and drainage patterns
• Soil report (if available) — tells you what you’re dealing with below the surface
• Project specifications — outlines compaction requirements, material standards, and any special conditions
• Utility plans — you need to know what’s in the ground before you dig

If you’re bidding a job without a grading plan, you’re guessing. That’s fine for small residential work you can walk yourself, but for anything larger, get the plans.

Step 2: Understand the Site Conditions

Walk the site before you estimate it. Plans tell you a lot, but they don’t tell you everything:

• Existing vegetation — how much clearing and grubbing is involved? Mature trees cost more to remove than scrub brush.
• Soil conditions — is it sandy loam, clay, rock? Clay cuts slow, compacts firm, and swells when excavated. Rock changes everything.
• Site access — can a full-size excavator and tri-axle trucks get in and out cleanly, or is access tight?
• Drainage — where does water go during construction? Poor drainage means delays, which means money.
• Existing structures — are there old foundations, buried debris, or underground tanks? These are scope killers if you don’t find them first.

A 30-minute site visit can save you from a $20,000 mistake.

Step 3: Calculate Your Cut and Fill Quantities

This is the core of any dirtwork estimate. Cut is dirt you’re removing; fill is dirt you’re adding. The goal is to figure out how much of each you have.

The basics:

• Pull the existing and proposed grades from the grading plan
• Calculate the volume of material to be moved in cubic yards (CY)
• Common method: grid method or average end area method

Don’t forget swell and shrinkage:

• When you excavate soil, it expands (swells) — typically 10–30% depending on soil type
• When you compact fill, it shrinks — bank measure ≠ compacted measure
• A bank cubic yard of common earth becomes roughly 1.25 loose CY in a truck, and compacts back to about 0.90 CY

If you ignore these factors, your haul quantities and fill volumes will be off — sometimes way off.

On-site vs. off-site material:

• Ideally, your cut material can be used as fill elsewhere on the site (mass haul). This saves you import and export costs.
• If you have excess cut, you’ll need to haul it off — factor in trucking and tipping/disposal fees.
• If you’re short on fill, you’ll need to import — factor in material cost plus delivery.

Step 4: Estimate Equipment Hours

Once you know your quantities, figure out what equipment you need and how long it’ll take.

Common equipment for sitework:

• Excavator (for digging, trenching, demo)
• Dozer (for spreading, rough grading)
• Motor grader (for fine grading)
• Compactor (sheepsfoot for subgrade, vibratory drum for base)
• Scrapers (for large open sites with long haul distances)
• Dump trucks (for material hauling)

Production rates vary widely by equipment size, soil type, and operator skill, but here are rough starting points:

Calculate: Quantity ÷ Production Rate = Equipment Hours

Then add buffer for mobilization, moves between areas, and setup time — typically 10–15%.

Step 5: Price Your Equipment

For each piece of equipment, you need an all-in hourly cost. This includes:

• Ownership costs (depreciation, interest, insurance) — if you own it
• Operating costs (fuel, oil, maintenance, tires/undercarriage wear)
• Operator wages + burden (payroll taxes, benefits, workers’ comp)

If you’re renting, use the rental rate plus delivery/pickup, and add your operator separately.

Don’t just use the rental rate and forget the operator. That’s a common mistake that blows up labor budgets.

Step 6: Add Trucking Costs

Hauling is often one of the biggest line items on a sitework job. Factor in:

• Number of loads — based on your swell-adjusted loose volume and truck capacity
• Cycle time — load time + haul distance ÷ speed + dump time + return
• Number of trucks needed — to keep the excavator or loading equipment productive
• Disposal or material costs — tipping fees for unsuitable material, cost of imported fill or aggregate

A truck sitting in line waiting to load is a truck costing you money without producing anything. Size your truck fleet to match your loader’s output.

Step 7: Calculate Subgrade and Compaction Work

Most site grading specs require compaction to a certain density (commonly 95% of modified Proctor). Price this out:

• Number of passes required by equipment type
• Moisture conditioning if soil is too dry or too wet
• Proof rolling and any soft spot repairs (have a contingency for this)
• Testing costs if required by spec

Step 8: Don’t Forget the Indirect Costs

This is where a lot of small contractors leave money on the table. Your estimate needs to include:

• Mobilization and demobilization — getting equipment to and from the site
• Erosion control — silt fence, inlet protection, seeding (often spec’d and inspected)
• Dewatering — pumps, discharge lines, permits if needed
• Surveying/staking — who’s setting grade stakes?
• Project management time — your time has a cost
• Bonds and insurance — if required by the contract

Step 9: Apply Overhead and Profit

Once you have your direct costs totaled, apply your overhead markup and profit margin.

A common mistake is treating profit as an afterthought — something left over after everything else. It’s not. It’s a line item you build in from the start.

• Overhead covers your fixed costs: office, truck payments, insurance, admin staff, software subscriptions, etc. Know your overhead rate as a percentage of revenue.
• Profit is what you pay yourself for risk and what grows the business. Don’t work for free.

If you don’t know your overhead rate, that’s a separate problem worth solving — but as a rough starting point, many small sitework contractors target 10–20% combined overhead and profit on top of direct costs.

Step 10: Review Before You Submit

Before the bid goes out:

• Check your math — quantity takeoffs and arithmetic errors are common and costly
• Re-read the scope — make sure you haven’t missed a spec item or included work that isn’t yours
• Check the schedule — are there liquidated damages? Can you actually complete the work in the time allowed?
• Know your assumptions — write them down so you can defend your number if the owner pushes back

The Bottom Line

Dirtwork estimating isn’t guesswork — it’s a process. Site conditions, accurate quantity takeoffs, realistic production rates, and fully-loaded cost rates are the foundation. Miss any one of them and your bid is built on sand.

The contractors who win jobs at the right price — and actually make money when they finish — are the ones who follow a consistent process every time, whether the job is $20,000 or $2 million.

Estimating software built for contractors can help you move through this process faster and with fewer errors. If you’re still running bids on spreadsheets, it might be worth seeing what a purpose-built tool can do for your workflow.