Work out trench or pit excavation quantity by the mean-area method with the side slope of your choice, convert compacted fill into the loose quantity you must actually arrange, and understand how the schedule pays for extra lead and lift.
Both calculators run entirely in your browser — nothing is sent anywhere. Enter dimensions in metres; results come out in cubic metres (and cft alongside).
Enter the bottom dimensions of the cut and the depth. If the sides are battered, pick the slope and the calculator widens the top faces by 2 × slope × depth, then averages the two areas — the way most works offices record it in the details of measurement.
With a side slope of s : 1 (horizontal : vertical), each face of the cut steps out by s × D at ground level, on both sides. The plan area therefore grows from the bottom to the top, and the volume is taken as the depth times the average of the two areas:
The mean-area figure reads marginally on the higher side compared with the exact prismoidal formula; for ordinary trenches and pits the difference is a fraction of a percent, which is why the simpler average is the customary record entry. For very deep or very large pits some departments insist on the prismoidal formula — check your manual.
Fill is measured and paid compacted in place, but soil is carted and stacked loose. Enter the compacted fill volume from your details of measurement and the loose-to-compacted factor for the borrow material to see how much loose earth to arrange.
When soil is dug out it bulks; when it is placed back in layers, watered and rammed or rolled, it compacts to less than its loose volume. The factor you enter is simply the ratio of the two states:
Use the factor established by field trials or your department's practice for the actual borrow material — clayey soils bulk more, clean sands hardly at all. Remember the payment item remains the compacted quantity; the loose figure is only your arrangement (carriage and stacking) planning number.
Every earthwork rate in a schedule of rates is built for a stated initial lead (the horizontal distance the spoil is carried) and a stated initial lift (the height through which it is raised). Move the earth farther, or raise it higher, and the labour involved goes up — so the schedule provides separate extra items that are added on top of the basic excavation or filling rate. Getting these extras right is a routine part of preparing the abstract of cost and, later, of checking an RA bill.
Only the quantity that actually travelled the longer lead or climbed the higher lift is billed under the extra item — not the whole excavated quantity. On a large site with several spoil heaps the earthwork is therefore split lead-wise in the measurement record, and each portion carries its own extras. In an RA bill the extra-lead and extra-lift items appear as ordinary schedule items with their own quantities, so a deviation on the parent excavation item usually drags a proportionate deviation in the extras with it — worth remembering when you prepare the deviation statement.