Acres per load is one division, and it is the one that matters
Hopper capacity in pounds divided by the rate in pounds per acre gives acres per load. A 1,500 lb hopper at 120 lb per acre covers 12.5 acres. That single number tells you more about how the day will go than the machine width does, because it sets the rhythm: how often you stop, where the tender needs to be, and whether a 40 acre field is three trips or eight.
Turning it into time needs the coverage rate. Fifteen feet at 5 mph is 9.09 acres an hour theoretically, and at 78 percent field efficiency that is 7.09 acres an hour, so 12.5 acres is about 106 minutes. That is a comfortable interval. Halve the hopper or double the rate and it becomes 53 minutes, which changes the logistics of the whole field rather than just adding a stop.
Three ways a hopper gets measured, and why they disagree
Capacity comes at you in three units and they do not convert cleanly without knowing the material.
| Given as | What you need to convert | Where it goes wrong |
|---|---|---|
| Pounds | Nothing | The plate figure is often the geometric volume, not what meters out cleanly |
| Bushels | Weight per bushel | Standard test weights are assumed; the actual seed can differ several pounds either way |
| Cubic feet | Bulk density of the material | Treated seed, blends and damp fertiliser differ from the published density by a lot |
The reliable move is to weigh it. Fill the hopper, weigh the machine, empty it, weigh again. That gives usable capacity for the material you are actually carrying, which is the only figure the arithmetic here can use honestly. Published density figures are a starting point for a first estimate and nothing more.
Metering rate: the check you can do without a scale
The calculator reports pounds per minute and pounds per thousand feet of pass. Both are useful for verifying that the machine is set anywhere near the rate you intend, without needing to weigh a whole load.
Pounds per thousand feet is the field-friendly one. It is the rate per acre times the width in feet times 1000, divided by 43,560. At 120 lb per acre on a 15 foot machine, that is 41.3 lb over a thousand feet of travel. Catch the output over a measured distance, weigh it, and compare. If the machine delivers 30 lb over that thousand feet, the setting is out by a quarter and no amount of planning arithmetic will fix it.
Ground-driven metering has its own trap: the calibration assumes the drive wheel turns a set amount per foot travelled, and slip in soft ground breaks that assumption in the direction of under-application. Check on the surface you will actually work.
Refills are the hidden half of the schedule
Field efficiency in this calculator deliberately excludes refills, because refills are countable and everything else is not. Turns, point rows and the slow lap go into the percentage; the stops go in separately with their own clock.
The reason to separate them is that they respond to completely different fixes. A poor efficiency percentage is fixed by field layout, headland width and machine setup. Refill time is fixed by logistics — where the tender parks, whether it moves with the machine, how the transfer happens. Twelve minutes a refill sounds trivial until a 40 acre field takes four of them and you have lost most of an hour that was never in the plan.
Notice too that the last load is almost never a full one. The calculator shows how much the final load actually needs, which is the difference between carrying a sensible amount back and carrying most of a hopper of blended material that now has to go somewhere.
What sets the rate is not on this page
The rate per acre is an input here, and it is an input everywhere it should be. Seeding rates depend on the crop, the variety, the seed size, germination percentage, the date, the seedbed and the target population. Fertiliser rates depend on a soil test, the crop, the yield goal, what the previous crop left behind, and in many places on a nutrient management plan that is a legal document rather than an agronomic preference.
Those decisions belong with a soil test, a seed tag, an agronomist, and your local extension service, in that order of specificity. What this page does is take a rate you already have and turn it into loads, minutes and pounds. Once you have the field time, the field capacity calculator will tell you where the rest of the day went, and the fuel use calculator puts a cost on the hours. The same load-and-refill arithmetic in liquid form, where the hopper becomes a tank and the rate becomes gallons per acre, is on the sprayer calibration calculator.
Questions people ask
Should I enter the hopper plate figure or a weighed figure?
Weighed, if you can get it. Plate and brochure capacities are usually geometric — the volume inside the box — and metering systems commonly stop delivering evenly before the hopper is genuinely empty, especially with anything that bridges or is slightly damp. The practical capacity is what you can load and meter out reliably, which on many machines is a few percent under the stated figure. Entering the optimistic number makes the acres per load optimistic and puts the refill later than it will really come.
Does the calculator handle a bulk density I do not know?
It cannot invent one, and guessing badly is worse than using the pounds mode. Bulk density varies a great deal: dry granular fertiliser blends, treated seed, small seeds and coated seeds all behave differently, and moisture moves the figure again. If you only have a volume, weigh a measured container of the actual material — a five gallon pail is 0.668 cubic feet — and divide. That takes a couple of minutes and turns a guess into a measurement.
Why is field efficiency separate from refill time?
Because they have different causes and different fixes. Field efficiency covers turns, point rows and the general slack of working a real field, and it is improved by layout and headland width. Refills are a logistics problem solved by where the tender sits and how fast the transfer is. Rolling them into one percentage hides which of the two is costing you the day. If you want the efficiency figure derived rather than guessed, the field capacity calculator counts the turns explicitly and reports the percentage that results.
Can I use this for a broadcast spreader?
Yes, provided you use the effective spread width rather than the throw distance. A spinner spreader throws material well past the width it spreads evenly, and the usable width is where the pattern still overlaps acceptably with the next pass. That width is found with collection pans laid across the swath, not from the brochure. Put the pan-verified figure in the width box and the arithmetic holds; put the throw distance in and every number on the page is optimistic by the same proportion.
How do I convert a price per ton into the price per pound field?
Divide by 2000. A product at $600 a ton is $0.30 a pound, and at 120 lb per acre that is $36 an acre of material. The calculator asks per pound because the rate is per pound, which keeps a units mismatch from hiding inside the cost line. If your material is priced per bushel, divide the bushel price by the weight per bushel you entered above.