Trench Volume Calculator
Calculate trench excavation volume using trapezoidal cross-section with truck load and excavation time estimates.
About this calculator
This calculator treats a trench as a trapezoidal prism: the cross-section is the average of Top Width and Bottom Width times Depth, and that area is multiplied by Trench Length to get Volume. Because the formula multiplies length and depth directly into the result, both carry full weight — doubling either one doubles Volume. Top Width and Bottom Width matter too, but only through their average, so a wide top with a narrow bottom (the normal shape for a sloped-wall trench in loose soil) contributes less area than the same top width held constant on both sides.
Volume Cu Yd divides the cubic-foot figure by 27 for ordering fill or paying disposal by the yard, Truck Loads assumes a 10-cubic-yard truck and rounds up so a partial load still counts as a dispatched truck, and Excavation Time assumes a standard backhoe production rate of 30 cu yd/hr. What it does not account for: shoring or trench box setup time, unstable soil that requires wider benching than you enter, rock or utility conflicts that slow digging below the assumed 30 cu yd/hr rate, or spoil pile footprint if the site is tight.
Inputs
Results
Volume
1,200 cu ft
≈ 23 hot tubs
Volume
44.44 cu yd
≈ 23 hot tubs
How to Use This Calculator
- Enter Trench Length and Depth in feet.
- Enter Top Width and Bottom Width separately — if the trench has sloped walls, make Top Width larger than Bottom Width to capture the extra area.
- Read Volume in cu ft and cu yd — use the cubic yard figure when ordering fill or paying for spoil disposal.
- Use Truck Loads (10 yd) to schedule haul trucks and Excavation Time to plan equipment rental.
- Feed the cu yd output into the Excavation Cost or Backfill Quantity calculators for budget estimates.
How the result changes with Trench Length
| Trench Length | Volume | Volume |
|---|---|---|
| 50 | 600 cu ft | 22.22 cu yd |
| 75 | 900 cu ft | 33.33 cu yd |
| 150 | 1,800 cu ft | 66.67 cu yd |
| 250 | 3,000 cu ft | 111.11 cu yd |
What each input means
- Trench Length
- Total length of the trench.
- Top Width
- Width of the trench at ground level.
- Bottom Width
- Width at the bottom of the trench.
- Trench Depth
- Depth from ground surface to trench bottom.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersTrench Length = 100, Top Width = 4, Bottom Width = 2, Trench Depth = 4 = 4 input(s) provided
- Calculate VolumeVolume1200 = 1200
- Calculate VolumeVolume44.44 = 44.44
- Calculate Truck LoadsTruck Loads5 = 5
- Calculate Excavation TimeExcavation Time1.48 = 1.48
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does the calculator ask for both a top and bottom width?
Because most trenches aren't rectangular — safety codes often require sloped walls in loose soil, which makes the top wider than the bottom. The engine averages the two widths to get the true cross-sectional area of that trapezoid, rather than assuming a uniform rectangular cut.
Which matters more: making the trench longer or deeper?
They carry equal weight in the formula — Volume is Length times the average width times Depth, so a 10% increase in Length changes Volume by the same amount as a 10% increase in Depth. Neither one is more important; both are multiplied directly into the result.
Why round Truck Loads up to a whole number?
A dump truck either makes the trip or it doesn't — 6.2 truckloads of spoil means 7 trucks dispatched, with the last one partially full. Rounding down would leave material on site with no truck scheduled to haul it.
Does the Excavation Time account for soil type or rock?
No — it assumes a flat 30 cubic yards per hour for a standard backhoe in normal soil. Rocky, saturated, or heavily compacted ground will excavate slower than this estimate, so treat Excavation Time as a best-case baseline rather than a guaranteed schedule.
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