Why use this calculator
Mixing errors are expensive in both directions. Too little product and the weeds survive, you pay for a second pass and you select for herbicide resistance. Too much and you risk crop damage, residue breaches in grain and a label breach, because in Australia the rate on the APVMA approved label is a legal instruction, not a suggestion.
The arithmetic is simple on paper and easy to get wrong at the tank on a windy morning with two units in play, millilitres per hectare on the label and litres in the tank. This calculator does the conversion once, shows the area each full tank covers, and sizes the final part tank so you finish the paddock without a leftover mix that has to be sprayed out or disposed of.
How to use it
- Enter the product label rate in millilitres per hectare, taken from the rate table on the label for your crop, weed and growth stage.
- Enter the spray tank capacity as the usable volume to your normal fill line.
- Enter the spray volume in litres per hectare that your calibrated boom actually delivers at your working speed and pressure.
- Enter the area to spray in hectares from your farm map or guidance records.
- Read the product per full tank first, then check the final part tank row before mixing the last load.
What each result means
- Product per full tank
- The volume of chemical to add to each full tank so every hectare sprayed receives exactly the label rate you entered.
- Area covered per full tank
- Hectares one full tank will cover at your calibrated spray volume, useful for planning refill points and runs.
- Water to add per full tank
- Tank capacity less the product volume, so the finished mix fills the tank to its line rather than overflowing it.
- Tank fills needed
- Total loads to finish the paddock, with the number of those that are full tanks shown in brackets.
- Final part tank
- Product and total mix volume for the last strip, so the final load is sized to the area left and nothing is wasted.
- Total product needed
- Chemical to have on hand for the whole job, which should be checked against the shed stock before you start.
- Total spray volume
- Total litres of mix the job uses, which sets how much clean water has to be carted to the paddock.
The formula
Area per tank
(ha) = tank capacity (L) divided by spray volume (L/ha)
Product per full tank
(ml) = label rate (ml/ha) multiplied by area per tank
Water to add
(L) = tank capacity minus product volume in litres
Full tanks = whole number of area per tank in the paddock area; the remaining hectares form a part tank holding label rate x remaining ha of product in spray volume x remaining ha of mix
Total product
(ml) = label rate x area
Total spray volume
(L) = spray volume per hectare x area
How this number is used in practice
On a broadacre farm the numbers that matter at the tank are product per load and the size of the last load. Most operators fill to the same line every time, so once the product per full tank is known it becomes a routine measure through the induction hopper.
The last load is where money and compliance go wrong: a full tank mixed for a ten hectare strip leaves thousands of litres of mix that has to be sprayed out somewhere, and spraying it over already treated ground is a double dose that the label does not allow. Sizing the final part tank to the remaining hectares avoids both problems.
The label rate is the legal ceiling and floor in Australia. The APVMA approves each product label, and state control of use laws require you to follow its rates, water volumes, withholding periods and buffer zones. Water rate matters as much as product rate: dropping from 80 to 50 L/ha to cover more ground per tank concentrates the mix and changes droplet coverage, which can reduce control with contact products.
Recalibrate the boom whenever you change nozzles, pressure or speed, and keep a spray record of the rate, volume, weather and mix for every job.
Worked examples
Knockdown at 1.5 L/ha, 3,000 L tank, 80 L/ha, 160 ha paddock
56,250 ml (56.25 L) per full tank, 5 fills with the last a part tank of 15,000 ml in 800 L for 10 ha, 240,000 ml (240.0 L) in total.
Selective at 700 ml/ha, 2,000 L tank, 100 L/ha, 45 ha
14,000 ml (14.00 L) per full tank, 3 fills (2 full), final part tank 3,500 ml in 500 L for 5 ha, 31,500 ml total.
Self-propelled sprayer, 6,000 L tank, 50 L/ha, 2 L/ha product, 600 ha
240,000 ml (240.00 L) per full tank covering 120 ha, exactly 5 full fills, 1,200,000 ml (1,200.0 L) total.
When people use it
- Measuring the product for each boomspray load before filling
- Sizing the last part tank so no mix is left over at the end of a paddock
- Ordering the total chemical for a spray program across several paddocks
- Planning water cartage and refill points for large paddocks
- Training new operators to check the mix sheet against the label
Tips
- Read the label rate for your exact crop, weed and growth stage. The label is legally binding and this tool only does the arithmetic.
- Calibrate the boom before trusting the spray volume. A worn nozzle set can put out 10 to 15 per cent more than the chart says.
- Half fill the tank with water, start agitation, then add products in the order the labels specify before topping up.
- Do a jar test before tank mixing two products for the first time to catch incompatibility before it blocks the filters.
- Record rate, water volume, wind speed, temperature and delta T for every job, as your state control of use rules require.
- Triple rinse drums at the hopper and add the rinsate to the tank so the product counts toward the load.
What it assumes, and where it stops being accurate
- The label rate is applied evenly across the whole area entered, with no allowance for overlap, headland double coverage or skips.
- Spray volume is the calibrated output of the boom at a constant speed and pressure.
- Product volume counts toward tank volume, so water to add equals tank capacity less product. Adjuvants are not included unless you add them to the rate.
- The tool does not check label restrictions such as maximum rates, water volume limits, buffer zones, withholding periods or tank mix compatibility.
- Rates in grams for granular or dry formulations can be entered as if they were millilitres, but the litre conversion then reads as kilograms.
Terms used on this page
- Label rate
- The approved amount of product per hectare printed on the registered label, which is legally binding in Australia.
- Spray volume
- Total litres of mix applied per hectare, also called the water rate or carrier volume.
- Calibration
- Measuring actual nozzle output at a set speed and pressure so the spray volume is known, not assumed.
- Delta T
- The difference between dry and wet bulb temperatures, used to judge evaporation and drift risk before spraying.
Questions people ask
- Is the answer from this calculator a legal rate?
- No. In Australia the rate printed on the APVMA approved label is the legal instruction, and state control of use laws require you to follow it along with its water volume, buffer and withholding directions. This calculator only converts the label rate you enter into product per tank. Always check the result against the label before mixing.
- What spray volume should I use?
- Use the water rate on the label and the one your calibrated boom actually delivers. Broadacre herbicide work in Australia commonly runs 50 to 100 L/ha, while contact products, fungicides in dense canopies and horticulture often need more. Lowering the volume to cover more hectares per tank changes droplet coverage and can cut control.
- How do I convert a label rate in L/ha to ml/ha?
- Multiply litres by 1,000. A label rate of 1.5 L/ha is 1,500 ml/ha, and 800 ml/ha is 0.8 L/ha. For dry products labelled in grams or kilograms per hectare, enter grams per hectare in the rate box and read the litre figures in the results as kilograms instead.
- Why is the last tank a part tank?
- Paddocks rarely divide evenly into full tanks. The final part tank row gives the product and mix volume for the hectares left, so you mix only what is needed. Mixing a full tank for a small strip leaves surplus spray that must be disposed of lawfully and cannot be sprayed over treated ground.
- Can I mix several products in one tank?
- Often yes, but only where the labels allow it or permit tank mixes and the products are physically compatible. Add products in the order the labels state, usually water conditioners first, then dry formulations, then liquids and finally adjuvants. A small jar test with the same water source catches problems before they block filters.
Use this with
Spray Dilution Calculator answers one part of the question. These pick up where it stops: Cost Per Hectare Calculator, Fertiliser Application Calculator, Seed Rate Calculator and Crop Yield Estimator.
Where these figures come from
Figures and rules on this page follow Australian law and ATO guidance.
- Australian Pesticides and Veterinary Medicines Authority. Registers agricultural chemicals and approves the legally binding label rates
- Grains Research and Development Corporation. Spray application, farm budgeting, crop water use and phenology research for Australian grain growers
- NSW Department of Primary Industries. Farm budgets, drought feeding, fencing, farm dam and soil water guidance
Spray Dilution Calculator produces an estimate for general information. It is not financial, tax, medical, legal or engineering advice. read the full disclaimer. Spotted a wrong number? Report it and it gets fixed. The form picks up this calculator and the inputs you used.