How to Measure for Fence and Deck Stain

A fence and a deck need separate measurement records. A fence is measured by run and side, and a deck is measured by floor, stairs, and railing. Mixing the two into one total hides the part that was guessed, and the gallon count that follows it cannot be checked.

How do you measure a solid fence?

Measure each run separately, then add the runs. A run is one straight section between corners, gates, or changes in height.

One side area = run length × run height

Fence area = sum of run areas × sides stained

Measure height from the ground to the top of the boards, not to the top of a post cap unless the cap is also stained. Measure length along the fence line, following each run, rather than estimating from a property line or a lot size. Stain one side only when the other side belongs to a neighbour or is deliberately left unstained, and record that choice beside the total. Staining both sides doubles the area, and that single choice is the most common reason a fence order comes up short.

How do you measure a picket fence?

A picket fence has gaps, so length × height measures empty air as well as wood. Measure the wood itself: one picket, the posts, and the rails, then multiply by the counts.

One picket area = 2 × (face width × height) + 2 × (thickness × height) + (face width × thickness)

The first term covers the front and back faces, the second covers both vertical edges, and the third covers the top edge. Count every picket, post, and rail in the stained section. For a picket 3.5 inches wide, 0.75 inches thick, and 4 feet high, the faces give 2 × 0.292 × 4 = 2.34 ft², the edges give 2 × 0.0625 × 4 = 0.50 ft², and the top gives 0.292 × 0.0625 = 0.02 ft², for about 2.86 ft² per picket. Posts use the same idea on four sides, and rails are measured by length × exposed face height on each exposed side.

What about split-rail and shadow-box fences?

A split-rail fence is mostly open space, so a length × height total would order stain for gaps that hold no wood. Measure each post on its four sides and each rail on its exposed sides, then add them. Angi gives this post-and-rail method for split-rail fences for exactly that reason.

A shadow-box fence carries boards on both faces in an alternating pattern, so both faces hold wood even though each face looks partly covered. One trade guide applies a 1.5 multiplier to the flat length × height total for shadow-box fences. Treat that figure as a planning allowance from one trade guide, not a manufacturer factor, and label it as such in the record. When the board count is known, the picket component method above gives a checkable total without the allowance.

How do you handle gates, posts, and sloped ground?

Do not subtract a gate. A gate is stained wood: its boards, frame, and posts all take stain, and its hardware only adds work around it. Measure the gate as part of the run it sits in, with its own board and frame lines when the gate differs from the fence panels.

Posts and rails belong on their own lines even for a solid fence, because they are often the parts a flat length × height total already covers only partly. On a solid fence the flat total covers the board faces; add post faces that stand proud of the boards and any exposed rail ends as separate lines, and state whether they were included.

On sloped ground, measure each run separately. For a racked fence that follows the slope, use the average height of the run or split the run into short sections and measure each one. For a stepped fence, measure each step section at its own height and add the sections. One height applied to a whole sloped fence understates the high end and overstates the low end.

How do you measure a deck floor?

Split the floor into rectangles, measure each one, and add them. For a triangular section, use half the base × height. The Paint Calculator takes the resulting area, but the measurement record itself is what makes the result checkable.

Floor area = sum of (rectangle length × width) + sum of (½ × triangle base × height)

Measure the walking surface, including the area under a railing line and around fixed planters that will be stained around rather than removed. The floor total measures the footprint, and the footprint includes the small gaps between boards. That makes the floor total a slight overstatement of board top surface, which is conservative for ordering, and the gap width should be noted rather than adjusted away with an invented deduction.

How do you measure deck stairs and railings?

Stairs need their own line. Each step contributes one tread and one riser, so the area per step is the tread depth plus the riser height, multiplied by the stair width. Multiply by the step count, then add the exposed stringer faces when the stringers are stained.

Stair area = (tread depth + riser height) × stair width × step count

Railings are the hardest part to measure because one railing holds a top rail, a bottom rail, posts, and many balusters. Measure one repeating railing section by components and multiply by the number of sections when the railing is uniform. When that count is impractical, one trade guide uses a planning rule of 10 to 15 ft² per linear foot of railing, including balusters. That rule is a third-party planning estimate, not a manufacturer figure, so keep it on its own line and replace it with a component count when the railing run is long or the order is large.

Worked fence example

A solid fence runs 120 linear feet at a uniform 6 feet high, and both sides are stained.

1. One side: 120 × 6 = 720 ft².
2. Both sides: 720 × 2 = 1,440 ft².
3. Metric check: 1,440 × 0.09290304 = 133.78 m².

Result: 1,440 ft² (133.78 m²) of fence to stain, before any separate post-face line. At a first-coat rate of 150 to 200 ft² per gallon, the range is 1,440 ÷ 200 = 7.2 gallons to 1,440 ÷ 150 = 9.6 gallons, rounded up to 8 to 10 gallons for one coat. The rate range and its source are covered in the coverage section below; the measurement record itself is the 1,440 ft² total.

Worked deck example

A rectangular deck floor measures 16 feet by 20 feet, with one stair of 5 steps, each 4 feet wide, with an 11 inch tread and a 7 inch riser. Railing is kept as a separate planning line and is not folded into this total.

1. Floor: 16 × 20 = 320 ft².
2. Stairs: (11 + 7) inches = 18 inches = 1.5 feet; 1.5 × 4 × 5 = 30 ft².
3. Floor plus stairs: 320 + 30 = 350 ft².
4. Metric check: 350 × 0.09290304 = 32.52 m².

Result: 350 ft² (32.52 m²) of deck floor and stairs. At a first-coat rate of 150 to 200 ft² per gallon, the range is 350 ÷ 200 = 1.75 gallons to 350 ÷ 150 = 2.33 gallons, rounded up to 2 to 3 gallons for one coat. For the railing planning line, 28 linear feet of railing at the trade-guide rule gives 28 × 10 = 280 ft² to 28 × 15 = 420 ft², kept separate so the checkable 350 ft² total stays exact.

How do coverage rates turn area into gallons?

Divide the measured area by the coverage rate of the selected product, then round up to whole gallons. Use the product record for the stain actually bought, because rates vary widely by product and by surface. A smooth board and a rough-sawn board do not share a rate even for the same product.

A second coat covers more area per gallon than the first because the wood is already partly saturated, so do not order two coats at the first-coat rate. For the worked deck example, the TWP two-coat average gives 350 ÷ 125 = 2.8 gallons to 350 ÷ 100 = 3.5 gallons, rounded up to 3 to 4 gallons total for two coats of those products. Check the selected product record for its own coat count before applying that arithmetic to another brand.

Common fence and deck measurement mistakes

• Measuring one fence side and forgetting the second side.
• Applying length × height to picket, split-rail, or shadow-box fences without a component or allowance method.
• Subtracting a gate as though it were an opening like a window.
• Using one height for a whole sloped fence instead of measuring each run.
• Counting deck treads and forgetting risers, stringers, fascia, and skirt boards.
• Treating railing as free because the floor area was measured.
• Using a siding or paint coverage rate for stain, or a fence stain rate for a deck floor.
• Ordering two coats at the first-coat rate.
• Recording one combined fence-plus-deck total that no one can re-measure.

Safety and professional scope

Measurement does not select the stain, the preparation method, or the application method. Follow the product label for surface preparation, temperature limits, recoat timing, and the surfaces the product is rated for, and follow the project safety plan for work at height, around power lines, and on wet or uneven ground. Stain products have their own ventilation and disposal instructions on the label and safety data sheet.

For a related measurement method, use the exterior siding measurement guide when the same project also includes siding, and keep the siding area on its own line rather than adding it to the fence or deck total.