How-To Guides · For farms

Measuring Compost Windrows, Manure Piles and Silage Without a Drone

October 24, 2026 · 8 min read

Farm piles get measured for nutrient plans, feed budgets, compost sales and program paperwork. Here are the extension-service tape methods for round piles, windrows and silage, the densities that turn volume into tons, and how a phone scan does the same job in a few minutes.

In short

For a round pile, measure the base circumference, divide by π for the diameter, estimate the height, and use the cone formula.
For a rounded windrow, volume ≈ 0.785 × height × top length × width, plus a partial sphere for the two ends. Alberta Agriculture’s worked example comes to 203 m³, about 266 yd³.
Silage piles are counted in tons of dry matter: cubic feet × a packed density of roughly 15 lb DM/ft³, then ÷ 0.35 for tons at 65% moisture.
Bulk density moves more than volume does. Compost windrows have been measured anywhere from 354 to 810 kg/m³ (about 600–1,370 lb/yd³). Weigh a pail of your own material.

Why farms measure piles

A manure pile is a nutrient budget waiting to be spread. Alberta Agriculture’s guide on estimating manure inventory opens by saying the weight or volume of available manure should be determined before land application, because application rates, storage capacity checks and the records a nutrient-management plan asks for all start from that number.

Compost is sold by the cubic yard, so the pile is the inventory. Silage is the winter’s feed, so the pile is the budget that decides whether you buy forage in February. And in 2020 the Coronavirus Food Assistance Program paid on tons of silage in piles, which sent a lot of farmers out with tape measures and a University of Wisconsin spreadsheet.

Measuring a round manure or compost pile

The Alberta method needs a tape, a board and a calculator. Walk the base of the pile with the tape to get its circumference, then divide by π for the diameter. Their example pile measures 22 m around, so its diameter is 22 ÷ 3.1416 = 7.0 m.

Height is the hard part, because you cannot stand on the pile. Their trick is a leaning 2×4: lean a 4.9 m board against the pile, mark a point on it 2.0 m from the ground end that sits 0.9 m above the ground, and the ratio 0.9 ÷ 2.0 = 0.449 applies to the whole board, so the pile is 4.9 × 0.449 ≈ 2.2 m high.

Then treat the pile as a cone: ⅓ × π × radius² × height = ⅓ × 3.1416 × 3.5² × 2.2 ≈ 28 m³, or about 37 cubic yards. Domed and flat-topped piles need the frustum formula in the stockpile volume formula guide.

Compost windrow volume: the extension formula

A windrow is a long pile with rounded ends, and the Alberta guide measures four things: the bottom length along the ground, the top length along the crest (always shorter), the width, and the height. The middle of the windrow is treated as a partial cylinder:

Volume ≈ 0.785 × height × top length × width. Their example windrow is 2.6 m high, 24 m along the top, 31 m along the ground and 3.4 m wide, so the cylinder part is 0.785 × 2.6 × 24 × 3.4 ≈ 166.5 m³. The two rounded ends together form a partial sphere whose diameter is (bottom length − top length + width) ÷ 2 = (31 − 24 + 3.4) ÷ 2 = 5.2 m, and whose volume is 0.131 × height × (4 × height² + 3 × diameter²) ≈ 36.8 m³. The whole windrow is about 203 m³, or 266 cubic yards.

A freshly turned windrow with a sharp crest is closer to a triangular prism: ½ × width × height × length. Whichever shape you pick, measure width and height at three places along the row and average them.

Silage piles: from cubic feet to tons

Silage is bought, sold and fed by weight, so the volume is only a step on the way. The University of Wisconsin’s pile capacity spreadsheet takes the bottom length without the ramps, the length of the filling ramp and the back ramp, the bottom width, the depth, the dome height and the top width of the dome, and works out the trapezoidal volume for you. Its default packed density is 15 lb of dry matter per cubic foot, close to the 14.5–14.8 lb DM/ft³ measured in well-packed Wisconsin bunkers.

Multiply cubic feet by that density to get pounds of dry matter, convert to tons, then divide tons of dry matter by 0.35 to get tons of silage at 65% moisture. The spreadsheet’s own example turns 508 tons of dry matter into 1,451 tons of silage. A British Columbia crop-insurance form does the same arithmetic the other way, cubic feet × 35 lb as-fed × percent dry matter ÷ 2,000.

Density is where silage piles go wrong. Wisconsin Extension’s bunker and pile guidance ties density to packing weight and fill speed, and recommends a minimum face removal of 4 inches a day for corn silage and 6 for hay silage, doubled for design, so a pile that is fed slowly loses dry matter you already counted.

Bulk density: the number that moves the most

Volume is geometry; weight is geometry times density, and density is where farm materials vary most. A 2002 study of compost windrows in the journal Horticultural Science measured three mixes at 354, 654 and 810 kg/m³ before turning, and found turning dropped each by 20–30% for a while. The lightest was grass and straw; the heaviest was half soil.

Material	Measured bulk density	Per cubic yard
Grass- and straw-heavy compost windrow	354 kg/m³	≈600 lb (0.30 US tons)
Fruit-pomace compost windrow	654 kg/m³	≈1,100 lb (0.55 tons)
Soil- and bark-heavy compost windrow	810 kg/m³	≈1,365 lb (0.68 tons)
Finished compost, typical range	590–950 kg/m³	1,000–1,600 lb (0.5–0.8 tons)
Solid cattle manure (Alberta pail example)	≈970 kg/m³	≈1,640 lb (0.82 tons)
Corn silage, 65% moisture, 15 lb DM/ft³	≈690 kg/m³	≈1,160 lb (0.58 tons)

Compost figures from the Horticultural Science study; manure from the Alberta guide; silage from the Wisconsin default. Your own pile will differ, mostly with moisture.

The Alberta guide’s answer to the variation is a 20-liter pail. Fill it from the pile, weigh it (their example: 19.48 kg), and the bulk density is weight ÷ volume, about 974 kg/m³. Total weight in tonnes is then bulk density × cubic meters ÷ 1,000. Our cubic-yard density table covers the other materials a farm handles, from topsoil to wood chips.

Scanning a farm pile with your phone

Every formula above assumes a shape the pile does not quite have. A phone scan skips the assumption: you walk around the pile while the app takes photos, it builds a 3D surface of what is actually there, and it reports the volume between that surface and the ground. Stockpile Scan does this on any iPhone running iOS 18 or later, free, with the result shown as a volume and a ± range worked out from that scan, and you can type in the density from your pail test for the weight.

A long windrow means walking down one side and back up the other, keeping the whole cross-section in view, which takes two or three minutes for a 25-meter row. Manure and wet compost are dark and low in contrast, so scan in daylight and not into a low sun. Scan either before or after turning, and do the same every time, since turning changes the volume by a quarter without changing the tons. Keep well clear of the turner and the loader, and scan a silage face when nobody is feeding out. The guide to every stockpile measurement method covers the trade-offs against a drone or a survey.

Keep the record

Whatever method you use, write down the date, the dimensions or the scan, the density you used and how you got it, and a photo. A nutrient plan wants the volume before spreading and where the pile sat. A compost buyer wants the dated volume and the border you measured to. A program or an insurer wants the measurements they can recompute. A PDF report with the plan view, the photos and the density assumption does all three jobs at once.

Frequently asked questions

How do you calculate the volume of a compost windrow?

Measure the bottom length along the ground, the top length along the crest, the width and the height. For a rounded windrow the extension formula is 0.785 × height × top length × width, plus a partial sphere for the two rounded ends whose diameter is (bottom length − top length + width) ÷ 2. For a sharply peaked windrow use ½ × width × height × length. Multiply cubic meters by 1.308 to get cubic yards.

How many tons of silage are in a pile?

Multiply the pile’s volume in cubic feet by its packed density. Extension spreadsheets default to 15 lb of dry matter per cubic foot, then divide tons of dry matter by 0.35 to get tons of silage at 65% moisture. A block 100 by 40 by 12 feet is 48,000 cubic feet, about 360 tons of dry matter and roughly 1,030 tons as fed. Real piles have sloped sides and ramps, so use the spreadsheet geometry or a scan rather than a box.

What is the bulk density of compost?

It depends on the feedstock and moisture. Compost windrows measured in one study ranged from 354 to 810 kg/m³, which is roughly 600 to 1,370 lb per cubic yard, and finished compost commonly runs 1,000 to 1,600 lb per cubic yard. Turning fluffs a windrow and lowers its density by 20 to 30 percent for a while. The reliable number is the one you measure by weighing a pail of your own material.

Can I measure a manure pile with my phone?

Yes. Walk once around the pile with a scanning app that builds a 3D model from photos, and you get a volume with a ± range and can enter your own density for the weight. Walk the whole way around in daylight with the entire pile in frame. A pile pushed against a wall or under a roof edge can’t be fully circled, so the hidden side still needs a tape estimate.

Measure your next pile with your iPhone

Stockpile Scan is free, with no ads, subscriptions or account. Walk around a windrow or manure pile and get its volume, a ± range, a weight estimate at your own density and a PDF report, all on the phone.

Download on the App Store

Any iPhone with iOS 18 or later. LiDAR optional. Learn more about the app.