Calculator
Example data table
| Scenario | Trim length | Width | Coats | Profile | Waste | Coverage | Estimated to buy |
|---|---|---|---|---|---|---|---|
| Potting shed + door + 2 windows | 110 ft | 3.5 in | 2 | 1.10 | 10% | 350 sq ft/gal | 0.75 gal |
| Raised bed edging set (metric) | 65 m | 90 mm | 2 | 1.20 | 12% | 10 m²/L | 2.0 L |
| Greenhouse trim refresh | 180 ft | 4 in | 2 | 1.35 | 15% | 325 sq ft/gal | 3.0 gal |
Formula used
This tool estimates paint from trim length and visible face width.
- Total length:
L = Lbase + Ltop + Lmisc + Ndoor·Ldoor + Nwin·Lwin - Flat area (one coat):
Aflat = L · WwhereWis trim face width in feet or meters. - Effective area:
Aeff = Aflat · Profile · Coats · (1 + Waste) - Paint needed:
Paint = Aeff / Coverage - Rounding: Imperial rounds up to the nearest quart. Metric rounds up to 0.5 L.
Profile factor increases area to reflect grooves, edges, and texture.
How to use this calculator
- Select your units first, then measure trim length.
- Enter baseboard, top trim, and any extra straight pieces.
- Add door and window counts if you want casing included.
- Set trim face width, coats, and a profile factor.
- Use coverage from the can label and add waste percent.
- Press Calculate to see paint, containers, and costs.
- Download a CSV or PDF for your project notes.
Measure trim like a production estimator
Trim work on sheds, pergolas, and greenhouse frames is length based. Walk the perimeter and record straight runs separately from casings. For doors and vents, count openings and measure a typical casing loop. Include lattice borders, fascia edges, and rails that are easy to forget. When lengths are uncertain, round up to the next foot and note it for verification.
Convert linear feet to paintable area
Paint demand comes from area, so the calculator converts linear footage into square footage using the visible face width. A 3.5‑inch board exposes about 0.292 feet of face. Multiply total trim length by face width to estimate area. Profiles add surface, so a profile factor covers bevels, grooves, and routed edges that raise area without changing length.
Coverage, coats, and substrate behavior
Coverage on the label assumes a smooth, sealed surface. Rough cedar, weathered fascia, or porous primed wood can reduce spread rate. Enter the coverage that matches your product and reduce it if the substrate is thirsty. Multiple coats scale demand linearly, so two coats doubles the requirement. If you switch to stain or enamel, update coverage and container cost.
Waste, containers, and batch planning
Waste is not just spills. It includes roller saturation, brush loading, tray loss, touch‑ups, and leftover paint you cannot buy in perfect fractions. A 10–15% waste allowance is common for trim because cutting-in creates extra handling. The calculator rounds to whole containers, helping you choose quart, gallon, or liter packaging. For consistent color, plan one batch for connected runs. Label lids with purchase date.
Quality control for exterior garden trim
Good results come from preparation and timing. Clean mildew, sand glossy spots, and spot-prime bare wood before topcoats. Paint when surfaces are dry and temperatures stay within the manufacturer’s range. Keep a wet edge on long runs, and back-brush sprayed sections around joints. After curing, inspect corners and end grain, then schedule a maintenance coat before peeling starts.
FAQs
Should I measure both sides of trim boards?
Only measure the faces you will paint. Most installed trim exposes one face, but some garden frames show two. If you will coat multiple faces, either increase face width or add extra length to represent the additional exposed area.
What is the profile factor and when do I change it?
Profile factor increases area for beveled, grooved, or ornate trim. Use 1.00 for flat boards, 1.10–1.25 for modest profiles, and higher for deep routed details. If you can wrap a tape around the profile, increase the factor.
How do I choose a realistic coverage rate?
Start with the manufacturer label value, then adjust downward for rough or weathered wood. Test a small section: track how much paint covers a known area. If coverage is lower than expected, update the input and recalculate.
Does primer count as a coat in this calculator?
This calculator estimates topcoat paint. If you also need primer, run the calculator again with primer coverage and cost, using the same area and coats. Many projects use one primer coat and one or two topcoats.
How much waste should I add for small trim jobs?
For careful brush work on small garden projects, 8–12% is typical. For lots of cut-ins, color changes, or windy outdoor conditions, 12–20% is safer. If you expect touch-ups later, keep a little extra.
Can I estimate cost if I buy paint in quarts and gallons?
Yes. Set the container size and price to match the package you plan to buy, then compare scenarios. Try quarts for small projects and gallons for long runs. The rounded container count shows what you must purchase.