FORMULA SHELF
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The arithmetic behind the work: what to measure, what to type in, and what the answer comes out as. Every formula says what the symbols mean and gives a worked example, so you can check it against a job you have already done.
SHELVES
Measurement
2 formulas
Used for round tanks, silage pits, feed bins, pipe ends and round bales. Measure the diameter, halve it for the radius.
A tank of 2 m diameter: r = 1 m, A = 3.14 m2 of base.
Convenience only. Double-check the result against the worked example or a second method before you use it.
For wedges, gussets, triangular yard patches, roof end bays and the spread of a spray boom on a slope.
A 10 m base with 4 m of height = 20 m2.
Convenience only. Double-check the result against the worked example or a second method before you use it.
Agronomy
3 formulas
Turn a spacing into a population, then into a seed rate. Work out what you want first, and the drill setting second.
Rows 30 cm apart with plants 10 cm apart in the row = 333,333 plants a hectare.
Lime is the one thing you cannot take back once it is spread, so use a buffer test rather than a pH test. See Soil Ph And Lime.
Buffer pH 6.5, target 6.5, 20 cm deep: no lime needed. Buffer 6.0 means about 0.4 t/ha on that soil.
To work out how long it takes to drill a field, how much fuel you will burn, or how much fertiliser to put on through the drill.
Rows 25 cm apart = 40,000 m of row a hectare.
Livestock
1 formulas
Measure around the chest just behind the front legs (heart girth) and from the point of shoulder to the pin bone (body length), both in centimetres. Square the girth, multiply by length, divide by 300. Best for cattle; less accurate for very fat or very thin stock.
Girth 190 cm x length 150 cm: 190 x 190 x 150 / 300 = 1,805 kg estimate.
Convenience only. Double-check the result against the worked example or a second method before you use it.
Growing
6 formulas
Bed planning. Work out how many plants you want, divide the bed area by the number, and that is the space each one gets.
Brassicas at 60 cm: 1 / 0.6 x 0.6 = 2.8 plants a square metre, so about 0.4 m2 each.
How much compost to barrow across the plot. One wheelbarrow is about 60 litres, so a 10 m2 bed at 5 cm needs about 5 barrows.
A 2 m x 1.5 m bed at 5 cm: 3 m2 x 0.05 x 1,000 = 150 L, or about 2.5 barrows.
Every bed plan starts with this. A 10 m bed with rows 30 cm apart has 33 rows, and at 25 cm in the row that is about 1,300 plants.
A 10 m bed, 30 cm rows, 25 cm plants: 10 / 0.25 = 40 plants a row.
The quickest way to plan a bed or a border. Onions at 10 cm square give 100 a square metre; potatoes at 30 cm give 11.
Carrots at 5 cm in 15 cm rows: 1 / (0.15 x 0.05) = 133 a square metre.
For beans, beetroot, carrots and onions sown in a drill in a bed. Sowing three seeds in a station and taking the best one is often more reliable.
Onions at 3 cm: 33 seeds a metre, and at 0.05 g a seed that is 1.7 g a metre of row.
How to keep a small bed productive all season. Sow little and often, and swap a fast crop for a slow one when the space frees up.
A 3 m2 bed of radishes at 5 cm squares gives 120 plants, or 40 a sowing for three sowings.
Physics
1 formulas
The jack, the brake press, the loader bucket and the post hole rammers. A 10 cm piston moved with 100 N will lift 1,000 kg on a 1 m piston.
A 100 N push on a 10 cm2 piston lifts 1,000 kg on a 1,000 cm2 piston.
SOURCES & PROVENANCE
1 listed
This page is an AI-organised index. The label means the grouping and cross-links were compiled with AI; the information itself comes from the public-domain books, reports and manuals listed below. Open any source to read the local copy or follow the link to the original publication.