Estimate any load by multiplying its volume by its density and check it with a bucket: a 20-litre bucket holds about 20 kg of water, 15 kg of grain and 30 kg of gravel. A two-horse cart that carries 600-1,200 kg is therefore full at 40-80 buckets of grain but at only 20-40 buckets of gravel. Weigh a sample bucket of anything you load, because density changes with moisture and packing.
Part of Logistics & Load Planning
Working out what cargo weighs when there is no scale, using volume, density and a few memorised reference values.
You Cannot Manage A Load You Cannot Weigh
Every decision in load planning depends on weight: how many animals, how many carts, how many days of feed, which bridge. Without a scale, you estimate. The parent article, Logistics & Load Planning, says to memorise a few reference values and gives shortcuts: a 20-litre bucket of water weighs 20 kg, a 20-litre bucket of grain about 15 kg, and a 20-litre bucket of gravel about 30 kg.
The method has two parts. Calculation turns a volume into a weight with a density from Common Material Weights. Measurement checks the estimate against a known weight or a balance; see Improvised Weighing.
What You Need
- A 20-litre bucket and a way to know it holds 20 litres. Water at 1 kg per litre makes it a reference weight.
- A tape measure for the volume of heaps and stacks.
- A table of densities — the one in Common Material Weights.
Method: Estimate And Check
Step 1: Count the buckets Fill a bucket with the material, level it off, and note the weight from the shortcut list or from a balance.
Step 2: Scale up Multiply by the number of buckets, or compute the volume in cubic metres and multiply by density in kilograms per cubic metre.
Step 3: Compare with the limit Check the answer against the cart’s or animal’s capacity.
Step 4: Re-check on the load Weigh a sample from the actual load, since wet grain and packed gravel weigh more.
Worked Example: How Many Buckets Fill A Cart
Inputs: a two-horse cart with a capacity of 600-1,200 kg, from Carts and Wagons; the bucket values above.
- Grain at 15 kg per bucket: 600 / 15 = 40 buckets to 1,200 / 15 = 80 buckets.
- Gravel at 30 kg per bucket: 600 / 30 = 20 buckets to 1,200 / 30 = 40 buckets.
- Water at 20 kg per bucket: 600 / 20 = 30 buckets to 1,200 / 20 = 60 buckets, or 600-1,200 litres.
The cart is full by weight at the same moment its bed is only partly filled with gravel, so the bed looks emptier than it is.
Common Mistakes
- Judging by volume — gravel looks light and is not. Count buckets.
- Using dry values for wet material — wet grain, wet sand and green wood weigh more.
- Believing one density — each material has a range. Use the ranges in the table.
- Forgetting the container — a barrel or sack adds to the weight.
Safety
Lifting and overloading
A bucket of gravel at 30 kg is a heavy lift, and a cart loaded past its limit breaks axles and injures animals. Lift with the legs, share heavy items between two people, and weigh before you load.
What’s Next
- Learn next: Common Material Weights — the reference table
- Combine with: Load Distribution — where to put the weight