Weed Control Coverage Calculator
Calculate weed killer or pre-emergent herbicide needed for your lawn or garden from area size and product concentration.
Returns correct mix and total quantity.
Weed control product coverage calculates how much herbicide, pre-emergent granule, or mulch you need to treat a specific garden or lawn area, preventing under-application (ineffective) or over-application (plant damage, waste).
Core formula: Product Needed = Treatment Area ÷ Coverage Rate per Unit Treatment Area = Length × Width (in square feet or acres)
Unit conversions:
- 1 acre = 43,560 sq ft
- 1,000 sq ft = 0.023 acre
- Liquid rate: oz per gallon × gallons per 1,000 sq ft
Common weed control types and application rates:
Pre-emergent granules (prevents weed seeds from germinating):
| Product Type | Typical Rate |
|---|---|
| Corn gluten meal (organic) | 20 lbs per 1,000 sq ft |
| Pendimethalin granule | 2–3 lbs per 1,000 sq ft |
| Prodiamine (Barricade) | 1.5–2.3 lbs per 1,000 sq ft |
Liquid herbicides, post-emergent, which kill weeds that are already up:
| Product | Dilution | Coverage |
|---|---|---|
| Glyphosate (Roundup) concentrate | 2.5 oz per gallon water | 300 sq ft per gallon mix |
| Vinegar solution (organic, 20% acetic acid) | Undiluted | 50–75 sq ft per liter |
Mulch (physical suppression): Depth needed: 2–3 inches for effective weed suppression Cubic feet of mulch = Area (sq ft) × Depth (ft)
Worked example, and this is what the calculator above does
A 1,500 sq ft lawn treated with pendimethalin at 2.5 lb per 1,000 sq ft.
Product needed = (1,500 ÷ 1,000) × 2.5 = 3.75 lb
Enter 1,500 as the area and 2.5 as the application rate. If you also know what the bag covers, put that in as well and you get the number of bags on top, plus a cross-check: the two figures together imply how much product is in each container, and if that does not match the weight printed on it, one of the two numbers has been read off the wrong line.
Application timing
Pre-emergents must go down before soil temperature reaches 55°F (13°C) at a two-inch depth. Forsythia coming into bloom is the traditional signal and it holds up well. Apply it a fortnight late and you have wasted the whole bag: a pre-emergent works on seeds in the ground and does nothing at all to a weed that has already come up.
The other half of that rule catches people every spring. A pre-emergent stops grass seed germinating just as effectively as it stops crabgrass, so you cannot overseed and apply a pre-emergent in the same season. Pick one.
Post-emergents are the opposite: they need actively growing weeds and warm weather, and they do nothing to seeds still waiting in the soil.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
SuperGlobalCalculator is independently built and maintained. See how we build and verify our calculators.