Fence Stain Calculator
Fence stain gallons per coat and two-coat total.
What it does
Fence stain disappears into wood faster than paint math suggests. A 150 ft privacy fence at 6 ft, both sides, spans 1,800 sq ft, and at rough-sawn coverage that drinks 7.2 gallons a coat. Smooth planed boards sip near 400 sq ft per gallon while weathered rough-sawn manages 200.
The tool above runs FPL coverage math. Enter length, height, sides, and coverage, and it prints area, gallons per coat, and the two-coat total. Defaults give 7.2 and 14.4 gallons. Round up at the store; split batches band visibly across runs.
Forest Products Laboratory research sets the rates. Its exterior stain guide puts opaque first coats near 400 sq ft per gallon on smooth wood and 250 on rough-sawn, with natural finishes spanning 400-500 smooth down to 200-250 weathered. A Purdue-linked FPL bulletin covers fences, decks, and siding the same way.
Prep decides how far stain goes. Clean dry boards above 50 F with a rain-free day drink evenly; sun-baked or damp wood blotches and wastes the second coat. Spraying beats brushing for pickets, then back-brush to push finish into the grain.
How to use
- Enter the fence length in feet.
- Enter the board height.
- Pick 1 or 2 stained sides.
- Enter coverage: 250 rough, 400 smooth.
- Read gallons per coat first, then two-coat total.
- Buy whole gallons for color match.
Formula
- length
- Fence run in feet, 0 to 10,000.
- height
- Board height in feet.
- sides
- Stained faces: 1 or 2.
- coverage
- Sq ft per gallon by surface, 100 to 600.
FPL coverage: opaque first coat ~400 smooth, ~250 rough-sawn; natural finishes 400-500 smooth, 200-250 weathered.
Worked example
Example: 150 ft fence, both sides
Defaults: 150 ft privacy fence, both sides, rough-sawn coverage.
- Inputs: 150 ft long, 6 ft high, both sides, 250 sq ft/gal.
- Area: 150 x 6 x 2 = 1,800 sq ft.
- One coat: 1,800 / 250 = 7.2 gal.
- Two coats: 7.2 x 2 = 14.4 gal.
- Tool shows 7.2 gal/coat, 1,800 sq ft, 14.4 gal two coats.
Reference table
| Surface | Opaque stain | Natural finish |
|---|---|---|
| Smooth planed | about 400 | 400-500 |
| Rough-sawn | about 250 | 200-250 |
| Calculator band | 200-300 default | same band |
Limits
- Planning math only. Thirst varies board to board.
- Second coat coverage assumed equal; it runs higher.
- Spray waste and lap losses excluded.
- Color match across batches unmanaged.
Common mistakes
- Using smooth coverage on rough-sawn boards.
- Counting one side of a two-sided fence.
- Buying exact gallons without rounding up.
- Staining wet or sun-baked boards.
- Skipping the second coat on weathered wood.
Try it yourself
Quick checks. Answers sit tucked under each question.
100 ft fence, one side, 250 coverage?
Area 100 x 6 x 1 = 600. One coat 600 / 250 = 2.4 gal. Two coats 4.8 gal, buy 5.
50 ft picket, both sides, 300 coverage?
Area 50 x 4 x 2 = 400. One coat 400 / 300 = 1.33 gal. Two coats 2.67 gal, buy 3.
Questions
How is stain figured?
Length times height times sides over coverage. Here 1,800 / 250 = 7.2 gal a coat.
What coverage per gallon?
About 400 sq ft/gal smooth, 250 rough-sawn for opaque stain; penetrating finishes 200-500 by surface, per FPL.
How much for two coats?
Double one coat: 7.2 x 2 = 14.4 gal here. The second coat stretches slightly farther, so x2 stays safe.
What if I stain one side only?
Yes. One side halves the area: 100 x 6 x 1 at 250 needs 2.4 gal a coat.
Do I round up?
Round up to whole gallons; 4.8 buys as 5. Partial gallons rarely match across batches.
When should I stain?
Clean, dry wood above 50 F with no rain for a day. Stain fails on wet or sun-baked boards.
Sources
- USDA Forest Products Lab: Exterior Stains for Wood (FPL-GTR-106)
- USDA FPL / Purdue: Exterior Wood in the South (FPL-GTR-69)