Inputs
Choose units, fine-tune coverage, and estimate containers.
Formula used
This estimator normalizes units and applies coats, porosity, and waste.
required_gallons = gallons × (1 + waste_percent ÷ 100)
containers = rounding(required_gallons ÷ container_gallons)
Tip: Higher porosity means more absorption and more sealer.
How to use this calculator
- Measure the surface area you plan to seal.
- Enter the product coverage from the label.
- Select coats, then adjust porosity if needed.
- Add a small waste percent for edges and overlap.
- Choose container size to estimate how many to buy.
Example data table
Sample projects to show typical inputs and outcomes.
| Project | Area | Coats | Coverage | Porosity | Waste | Est. gallons | 1-gal containers |
|---|---|---|---|---|---|---|---|
| Raised bed trim | 120 sq ft | 2 | 250 sq ft/gal | 1.10 | 10% | 1.16 | 2 |
| Stone path | 180 sq ft | 1 | 200 sq ft/gal | 1.20 | 8% | 1.17 | 2 |
| Garden bench | 65 sq ft | 2 | 300 sq ft/gal | 1.00 | 5% | 0.46 | 1 |
| Deck steps | 140 sq ft | 2 | 225 sq ft/gal | 1.15 | 12% | 1.61 | 2 |
| Planter box set | 90 sq ft | 3 | 275 sq ft/gal | 1.10 | 10% | 1.19 | 2 |
Examples are illustrative; always check your product label.
Surface preparation and absorption
Clean, dry surfaces seal more predictably. Remove algae, loose fibers, and dust, then allow full drying time. Damp wood or stone can cut coverage because sealer rides on water and pools. For new lumber, light sanding reduces raised grain and improves uniform uptake. Mask planting beds and metal hardware so drips do not stain soil or rust.
Coverage rates and real-world adjustments
Label coverage is tested on smooth panels. Rough-sawn boards, porous pavers, and grout lines increase surface area and absorption. Use the porosity factor to model this. Typical ranges are 0.95–1.05 for sealed or very smooth surfaces, 1.10–1.20 for average decks, and 1.25–1.40 for very porous stone. When using a sprayer, overlap can lower effective coverage compared with brushing.
Choosing coats for durability
Two thin coats usually outperform one heavy coat, especially on exterior wood. A first coat penetrates and locks fibers; a second coat builds water resistance and UV stability. High-traffic garden steps may need an extra coat, while vertical surfaces can often stay at one or two. Watch the recoat window on the label; applying too soon can trap solvents, while waiting too long can reduce bonding. Always run a small test patch to confirm sheen and absorption.
Waste and edge planning
Waste percent covers roller loading, sprayer overlap, and cut-in work along borders. Tight layouts with many corners can add 10–15% waste, while open slabs may stay near 5–8%. If you are color-matching or using tinted sealer, rounding up reduces the risk of batch variation. Break large areas into zones and finish a full zone per mix session for consistent appearance.
Buying strategy and storage
Container rounding helps align to shelf sizes and prevents mid-job shortages. If price is entered, the cost estimate supports budgeting and comparing products by total applied area. Store unopened sealer out of direct sun, keep lids tight between coats, and follow disposal rules for leftover material. For best results, plan work for mild temperatures and stable weather so curing is not interrupted by dew or irrigation.
How do I pick a porosity factor?
Start at 1.00 for smooth, previously sealed surfaces. Use 1.10–1.20 for typical decking or concrete. Use 1.25–1.40 for porous stone, grout, or rough lumber. When unsure, test a small area and adjust.
Should I always round up containers?
Rounding up is safer for outdoor projects because edge work and absorption vary. It also avoids stopping mid-coat, which can cause lap marks. If storage is limited, use nearest rounding and add a small waste percent.
Does coverage change between brushing and spraying?
Yes. Spraying often increases overlap and mist loss, reducing effective coverage. Brushing and rolling usually deliver more product into the surface and can raise usage on porous materials. Use the waste percent to reflect your application method.
Can I seal damp wood or stone?
It is best to seal only when the surface is dry. Moisture can block penetration, create haze, or reduce adhesion. Follow the product’s moisture and weather guidance, and allow extra drying time after rain or irrigation.
How do I measure irregular garden areas?
Split the surface into rectangles, triangles, or circles, calculate each part, then add them together. For beds and paths, measure along the centerline and average the widths. Add 5–10% for curves and borders.
What does the waste percent include?
Waste accounts for roller loading, brush work on edges, overlap, drips, and small spills. It also covers minor measuring errors. Open, simple slabs may need 5–8%, while corner-heavy layouts may need 10–15%.