SettingsSettings for this calculationUS
Waste is set to 30% by hand. Pick a tier above to replace it, or keep your own figure.
Every horizontal member added together — handrail, base rail, any mid rail.
A balustrade with a handrail and a base rail over 10 m of run is 20 m of rail, not 10. Add the posts here too if they share the rails' section, or work them as a second pass if they do not.
The distance around the section — 4 × the side for square, π × the diameter for round.
This is the field that makes the answer right, and it is not the size of the section. A 40 mm box has a girth of 160 mm; a 40 mm tube has 126 mm; a 50 × 25 box has 150 mm. Measure it if the profile is moulded or fabricated: run a tape around it once and that is the number.
The uprights between the rails.
Usually the larger half of the work and the half that gets left out of a quick estimate. At the common 99 mm maximum gap, a 10 m run carries roughly fifty of them — and together they can hold more paintable surface than the rails above them.
Painted length of one upright.
The exposed length between the rails, not the overall bar before it was cut. Where balusters are set into a base rail, the buried part takes no paint but does want the primer to run down to it, which is a detail rather than a quantity.
Around one upright: four times the side for square bar, pi times the diameter for round.
Twisted, moulded and scrolled balusters have far more girth than their nominal size suggests, and an ornamental panel more again. Where they are decorative, measure around one with a tape and use that.
Finish coats at the spread rate below.
Two is normal over a sound primed surface. Count the primer separately: it is usually a different product at a different rate, and on bare or rusted metal it is the coat that decides whether the job lasts.
What the tin claims for one coat on a smooth surface.
Metal paints commonly rate 10 to 14 m² per litre on smooth steel. The tin's figure assumes a flat surface, and the waste allowance below is what turns it into a railing figure rather than the rate itself — keep the two separate so you can see which is which.
Far higher than a wall, because most of a railing is air.
Brushing a section means loading, cutting in and going back round; anything sprayed loses most of what passes between the balusters. Thirty per cent suits brush work on a plain railing, and fifty or more is normal for ornamental work or spraying. This is the honest place for the loss — do not bury it by lowering the spread rate, because then neither figure means anything.
Paint needed
0.301 gal
The balusters hold 70% of the surface here — the part a quick estimate leaves out. Check the girth with a tape.
- Rail surface
- 17.19 sq ft
- Baluster surface
- 40.63 sq ft
- Total surface, 2 coat(s)
- 115.63 sq ft
- Allowance at 30%
- 0.07 gal
- Quart tins
- 2 quarts
They open the calculator with your figures already in it
Metalwork and Railing Paint Calculator: 0.3006 gal — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Show calculation logicHide calculation logic
How this was calculated
Formula source(s)
- Metalwork is measured by girth: the paintable area of a run is its length times the perimeter of its section, since the brush travels around the profile as well as along it
- Section girths: round is pi times the diameter, square is four times the side, and rectangular or angle is twice the sum of the two dimensions
- Paint for one coat is the area divided by the spread rate; coats multiply it, and the loss on open metalwork is far higher than on a flat surface
Inputs used
- Length of rails
- 33 ft
- Girth of the rail section
- 6.25 in
- Balusters or pickets
- 50
- Baluster height
- 3 ft
- Girth of a baluster
- 3.25 in
- Coats
- 2
- Spread rate
- 500 ft²/gal
- Loss on open metalwork
- 30
Intermediate steps
- Rail surface
- 17.19 sq ft
- Baluster surface
- 40.63 sq ft
- Total surface, 2 coat(s)
- 115.63 sq ft
- Allowance at 30%
- 0.07 gal
- Quart tins
- 2 quarts
Confidence note: The balusters hold 70% of the surface here — the part a quick estimate leaves out. Check the girth with a tape.
What this calculation does not cover
- Girth is the whole answer and it is not the section size. A square box section has four times its side and a round tube pi times its diameter, so two railings of the same nominal size differ by more than a fifth in paint. Run a tape around the section rather than reading a catalogue.
- Primer is not counted. On bare, galvanised or rusted metal the primer decides whether the finish lasts, and each of those three wants a different one — an etch or mordant solution on galvanising, a rust-converting or zinc-phosphate primer on steel. None of them shares this page's spread rate.
- Preparation is not counted either, and on metalwork it is most of the work: wire-brushing, needle-gunning or blasting back to sound metal, and degreasing before anything is applied. Paint over mill scale or loose rust fails on schedule whatever the quantity.
- The loss allowance assumes brush work. Spraying an open railing loses most of what passes between the balusters, and the figure to use there is nearer half again — or a sheet behind the railing, which changes the job rather than the number.
- Ornamental sections are under-counted by any girth taken from a nominal size. Twists, scrolls, collars and cast panels can double the real surface, and the only honest measurement is a tape around a representative piece.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
Part of a bigger job
This trade is one line of a job takeoff. Run the whole job and every other trade comes back with it, off the same measurements.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-23 · v1.0.0
Regulatory standards & verification citations3
- Metalwork is measured by girth: the paintable area of a run is its length times the perimeter of its section, since the brush travels around the profile as well as along it
- Section girths: round is pi times the diameter, square is four times the side, and rectangular or angle is twice the sum of the two dimensions
- Paint for one coat is the area divided by the spread rate; coats multiply it, and the loss on open metalwork is far higher than on a flat surface
Cite this page
Your workspace
Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.
Protection this work requires
- Stop and check first. Paint under later coats in older housing can be lead-based, and sanding or heat-stripping it produces lead dust that is especially harmful to children and to anyone pregnant. Test before you disturb it — this is a job for a tested, controlled method, not a better mask.
Tools and safety for this job
To roll and cut in two coats and prepare a surface for paint. Generic types, no brands, no prices.
- Joint-compound dust is very fine and travels: a P1/FFP1 mask is the minimum, and a damp-sponge finish avoids most of it.
- A dust mask does nothing about solvent vapour: ventilate through, and use an organic-vapour (A1) cartridge respirator in an enclosed room.
- Most fatal falls on small jobs are from under three metres: use a tower or a ladder tied at the top, and never work off the top two rungs.
Show the 11 tools this job needsHide tools
Essential
Brushes
Dust sheets and masking
Filling knife
Roller frame, sleeves and tray
Scraper
Recommended
Caulking gun
Extension pole
Pole sander
Random orbital sander
Step ladder
Optional
Dust extractor or vacuum with a fine filter
Also needed as materials: abrasive discs, caulk and sealant cartridges, masking tape, plastic sheeting, roller sleeves, sanding screens or paper.
what each painting tool is for, and the spec that decides which to buy where one does.