Lawn Weed Control & Herbicide Rate Calculator

ANA›Life Services Authority›National Calculator Authority›Lawn Weed Control & Herbicide Rate Calculator

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Lawn Weed Control & Herbicide Rate Calculator

Calculate the exact amount of herbicide needed for your lawn based on product label rate, lawn area, and application method. Avoid over- or under-application for safe, effective weed control.

Lawn Area (sq ft)

Product Label Rate (fl oz per 1,000 sq ft)

Sprayer Tank Size (gallons)

Sprayer Output Rate (gallons per 1,000 sq ft)

Typical backpack/pump sprayer: 0.5–2 gal per 1,000 sq ft

Herbicide Concentration (% active ingredient on label)

Found on product label (e.g., 18.5% for many 2,4-D products)

Calculate

function lawCalc() { var resultDiv = document.getElementById('law-result');

var lawnArea = parseFloat(document.getElementById('law-lawn-area').value); var labelRate = parseFloat(document.getElementById('law-label-rate').value); var tankSize = parseFloat(document.getElementById('law-tank-size').value); var outputRate = parseFloat(document.getElementById('law-output-rate').value); var conc = parseFloat(document.getElementById('law-conc').value);

// Validation if (isNaN(lawnArea) || lawnArea ⚠ Please enter a valid lawn area (sq ft).'; return; } if (isNaN(labelRate) || labelRate ⚠ Please enter a valid label rate (fl oz per 1,000 sq ft).'; return; } if (isNaN(tankSize) || tankSize ⚠ Please enter a valid tank size (gallons).'; return; } if (isNaN(outputRate) || outputRate ⚠ Please enter a valid sprayer output rate.'; return; } if (isNaN(conc) || conc 100) { resultDiv.innerHTML = '⚠ Please enter a valid herbicide concentration (0.01–100%).'; return; }

// ── Core Formulas ────────────────────────────────────────────────────────── // 1. Total herbicide needed for entire lawn // totalHerbicide (fl oz) = (lawnArea / 1000) × labelRate var totalHerbicide = (lawnArea / 1000) * labelRate;

// 2. Total water (spray solution) needed for entire lawn // totalWater (gallons) = (lawnArea / 1000) × outputRate var totalWater = (lawnArea / 1000) * outputRate;

// 3. Number of full tank loads required // tankLoads = totalWater / tankSize var tankLoads = totalWater / tankSize; var fullTanks = Math.floor(tankLoads); var partialTank = tankLoads - fullTanks;

// 4. Herbicide per tank load // herbPerTank (fl oz) = labelRate × (tankSize / outputRate) // Derivation: each tank covers (tankSize / outputRate) × 1000 sq ft // herbicide for that area = labelRate × (tankSize / outputRate) var areaPerTank = (tankSize / outputRate) * 1000; // sq ft covered per tank var herbPerTank = labelRate * (tankSize / outputRate);

// 5. Herbicide for partial last tank var herbLastTank = herbPerTank * partialTank; var waterLastTank = tankSize * partialTank;

// 6. Active ingredient applied (oz) // AI (fl oz) = totalHerbicide × (conc / 100) // Convert to grams: 1 fl oz ≈ 29.5735 mL; density of water-based herbicide ≈ 1 g/mL var aiFlOz = totalHerbicide * (conc / 100); var aiGrams = aiFlOz * 29.5735;

// 7. Application rate check (lb AI per acre) // lawnAcres = lawnArea / 43560 // aiLbs = aiGrams / 453.592 // lbAIperAcre = aiLbs / lawnAcres var lawnAcres = lawnArea / 43560; var aiLbs = aiGrams / 453.592; var lbAIperAcre = lawnAcres > 0 ? aiLbs / lawnAcres : 0;

// 8. Dilution ratio (herbicide fl oz per gallon of water in tank) // dilutionRatio = herbPerTank / tankSize var dilutionRatio = herbPerTank / tankSize;

// ── Format helpers ───────────────────────────────────────────────────────── function fmt(n, d) { return n.toFixed(d !== undefined ? d : 2); }

var lastTankNote = ''; if (partialTank > 0.01) { lastTankNote = 'Last (partial) tank — water' + fmt(waterLastTank, 2) + ' gal' + 'Last (partial) tank — herbicide' + fmt(herbLastTank, 2) + ' fl oz'; }

var aiWarning = ''; if (lbAIperAcre > 4) { aiWarning = '⚠ Active ingredient rate (' + fmt(lbAIperAcre, 2) + ' lb AI/acre) is high — verify against label maximum before applying.

'; }

resultDiv.innerHTML = '### Results ' + '' + 'ParameterValue' + 'Lawn Area' + lawnArea.toLocaleString() + ' sq ft (' + fmt(lawnAcres, 3) + ' acres)' + 'Total Herbicide Needed' + fmt(totalHerbicide, 2) + ' fl oz' + 'Total Spray Water Needed' + fmt(totalWater, 2) + ' gallons' + 'Area Covered Per Full Tank' + fmt(areaPerTank, 0) + ' sq ft' + 'Herbicide Per Full Tank' + fmt(herbPerTank, 2) + ' fl oz' + 'Dilution (herbicide per gallon of water)' + fmt(dilutionRatio, 3) + ' fl oz / gal' + 'Number of Full Tank Loads' + fullTanks + '' + lastTankNote + 'Active Ingredient Applied' + fmt(aiFlOz, 2) + ' fl oz (' + fmt(aiGrams, 1) + ' g)' + 'AI Rate' + fmt(lbAIperAcre, 3) + ' lb AI / acre' + '' + aiWarning + 'Always read and follow the product label. Never exceed the maximum labeled rate.

'; }

#### Formulas Used

1. Total Herbicide (fl oz) Total Herbicide = (Lawn Area ÷ 1,000) × Label Rate

2. Total Spray Water (gal) Total Water = (Lawn Area ÷ 1,000) × Output Rate

3. Herbicide Per Tank Load (fl oz) Herb/Tank = Label Rate × (Tank Size ÷ Output Rate) Derived from: each full tank covers Tank Size ÷ Output Rate × 1,000 sq ft

4. Number of Tank Loads Tank Loads = Total Water ÷ Tank Size

5. Active Ingredient Applied (fl oz) AI = Total Herbicide × (Concentration % ÷ 100)

6. AI Rate (lb AI/acre) lb AI/acre = (AI in grams ÷ 453.592) ÷ (Lawn Area ÷ 43,560)

7. Dilution Ratio (fl oz herbicide per gallon of water) Dilution = Herb/Tank ÷ Tank Size

#### Assumptions & References

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References

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