Turn a spreading plan into material you can handle
A field plan may say to spread a number of tonnes per hectare, short tons per acre, or a layer of compost of a certain depth. Before the work starts, you need to know the weight and volume to move. These are different measures: two piles can fill the same trailer yet weigh differently because their moisture and compaction differ.
This calculator starts with a rate or depth you already selected. It uses your material's as-applied bulk density to connect weight and volume. If you enter a usable load volume, it also estimates whole loads. Optional lab values show the total N, P₂O₅ and K₂O in that amount and, where you supply a factor, an estimate of what may be available in the first season. It does not decide how much your crop should receive.
How to use the calculator
Enter the field plan
Choose metric or US units. Select Material weight per area if your plan gives a mass rate, or Spread depth if it gives a uniform layer depth. Enter only the area you will treat. The rate or depth should come from your soil and crop plan, not from this calculator.
Describe the material you will spread
Enter its as-applied bulk density: the weight of the moist, ready-to-spread material in a known volume. A dry or old density value can give a misleading weight or volume. If you know the usable cubic metres or cubic yards carried in one load, open the optional section and enter that capacity.
Add lab figures only if they match this material
In the optional section, enter N, P₂O₅ or K₂O percentages from an as-applied or wet-basis analysis. For each nutrient, enter a first-season availability percentage only if you have a defensible material-specific estimate. Leave an unknown factor blank. Select Calculate material, then use the large weight result to prepare material and the volume or loads to plan hauling.
How the calculation works
The calculator first finds the total material for the area you entered. It then uses bulk density to connect weight and volume. Keep the rate, area and density in the same unit system; the unit selector handles conversions when you change it.
- Starting with a weight rate: total weight = treated area × planned material rate. In metric units, volume in m³ = total metric tonnes ÷ density in metric tonnes/m³. In US units, volume in yd³ = total US short tons × 2,000 lb/short ton ÷ density in lb/yd³.
- Starting with a depth: metric volume in m³ = area in ha × 10,000 m²/ha × depth in cm ÷ 100 cm/m. US volume in yd³ = area in acres × 43,560 ft²/acre × depth in inches ÷ 12 inches/ft ÷ 27 ft³/yd³. Multiply that volume by density to get metric tonnes, or multiply yd³ by lb/yd³ and divide by 2,000 to get US short tons.
- Optional loads: whole loads = volume ÷ usable volume per load, rounded up. A partial final load counts as one trip.
- Optional nutrients: total nutrient = as-applied material weight in kg or lb × lab analysis percentage ÷ 100. Convert metric tonnes to kg by multiplying by 1,000, or US short tons to lb by multiplying by 2,000. Estimated first-season available nutrient = total nutrient × your nutrient-specific availability percentage ÷ 100. If that percentage is blank, the available amount is not estimated.
The page keeps full precision for these steps and rounds the displayed weights and volumes to at most four decimal places in ordinary ranges. Whole loads always round up.
Check the bulk density before trusting a load estimate
Bulk density tells you how much a known volume of this material weighs. It is the bridge between the weight in a nutrient plan and the space needed in a truck or spreader. Use a recent, representative value for the moist material as it will be loaded. A figure from a dry product sheet or from a very different pile is not the same measurement.
If you measure it yourself, weigh a container of known volume both empty and filled with a representative sample. Subtract the empty weight, then divide by the filled volume. For example, 600 kg of material in 1 m³ is 0.6 metric tonnes/m³. Record whether the sample was loosely filled or compacted, and use a value that resembles your loading method. This measurement helps with planning; it does not replace a calibrated spreader check in the field.
Check a weight-rate plan
Suppose a plan covers 2 hectares at 5 metric tonnes of solid compost per hectare. That is 10 metric tonnes for the field. If the as-applied density is 0.6 metric tonnes per cubic metre, the volume is 10 ÷ 0.6, or about 16.6667 m³. A spreader that carries a usable 4 m³ per trip needs five loads; the final load is not full. These numbers describe the planned material amount, not an appropriate rate for a particular crop.
When you start with a weight rate, the field weight is area × rate. Volume follows from that weight and bulk density. The density must describe the same moist material you intend to load. A wetter or more compact batch can change the volume needed for a given weight.
Check a spread-depth plan
A depth describes a layer across an area. For 0.25 hectare at a planned 2 cm depth, the area is 2,500 m² and the layer volume is 2,500 × 0.02 = 50 m³. At 0.7 metric tonnes/m³, that is 35 metric tonnes. With an 8 m³ usable load, plan seven loads. In US units, one acre at one inch is about 134.4444 yd³ before density is applied.
This geometric calculation assumes a uniform, uncompacted layer over the whole entered area. Windrows, uneven spreading, shrinkage, settling and field losses can change the amount actually placed. A depth input is not a claim that the depth is suitable for the soil or crop.
Read total and first-season nutrients separately
A laboratory analysis tells you what is present in a sample. It does not say that every nutrient becomes available to the crop in one season. The calculator multiplies the as-applied material weight by each entered analysis percentage to show total nutrient mass. It then multiplies that total by your separately entered availability factor to show an estimated first-season amount. A blank factor deliberately produces “Not estimated.”
For example, the 10-tonne field amount above contains 10,000 kg of material. At 1.5% as-applied N, it contains 150 kg total N. With a separately justified 25% first-season availability factor, the estimate is 37.5 kg available N. A 1% P₂O₅ analysis yields 100 kg total P₂O₅; a 40% factor would yield 40 kg first-season available. The factors in this arithmetic example are not recommendations. Real availability depends on the material and field conditions.
Check the laboratory basis before entering percentages. Dry-basis percentages cannot be used here without a moisture conversion. Use N, P₂O₅ and K₂O on the same reporting basis as the crop plan; elemental P and K are different units. A manure rate aimed only at N can also supply more P or K than needed. Compare all relevant nutrients with your soil test and nutrient plan.
Know what a load count means
The load result is material volume divided by usable volume per trip, rounded up to a whole load. It is a hauling count, not a measure of safe payload weight. Check the trailer or spreader's weight limit separately because dense, wet material can reach that limit before its body is full. If volume capacity is unknown, leave the field blank and use the weight and volume results without a load estimate.
For a US-unit check, 2 acres at a planned 3 US short tons/acre means 6 short tons. At 1,200 lb/yd³, the 12,000 lb total occupies 10 yd³. A 3-yd³ usable load calls for four trips, with one partial load. If that material analyzes at 2% as-applied N, it contains 240 lb total N; a separately supported 50% first-season factor gives an estimate of 120 lb available N. Neither percentage is a default for manure.
Common mix-ups that change the answer
- Using a dry-basis lab percentage with wet material weight. Obtain the as-applied analysis or convert it outside this calculator with a reliable moisture measurement.
- Using a bag, trailer or purchase volume as the field area. The area field is only the land that will receive this plan.
- Reading total nutrients as first-season crop supply. Enter a separate, justified availability factor for each nutrient you want to estimate.
- Treating a whole-load count as a payload approval. Volume capacity and safe weight capacity are separate limits.
- Mixing elemental P or K with P₂O₅ or K₂O. Match the lab report and crop plan before comparing amounts.
Before spreading
Confirm that the material sample represents the batch being applied and that its bulk density was measured in a comparable condition. Confirm the planned rate against the crop, soil test, timing, site restrictions and local requirements. This page does not account for nitrogen loss, mineralization over later years, runoff, pathogens, food safety intervals or the calibration of a spreader. A field-scale allocation cannot replace that management work.