How much oil does softwood decking absorb?

Softwood (pine, spruce) is highly absorbent — the first coat uses approximately 0.20 L/m², which is 3-4 times more than dense hardwood. Subsequent coats absorb about 0.10 L/m² as the pores are partially filled. A 20 m² softwood deck with 2 coats needs roughly 6 litres of oil. Always apply oil to clean, dry timber for best penetration.

How often should I oil my decking?

Softwood decking needs oiling annually. Hardwood decking (oak, iroko) every 2 years. Dense tropical hardwoods (ipe, cumaru) every 2-3 years. South-facing decks in full sun may need more frequent treatment. The water bead test works well — pour water on the deck: if it soaks in rather than beading up, it's time to re-oil.

What is the best oil for decking in the UK?

For UK conditions, Osmo Decking Oil and Owatrol Aquadecks are top professional choices. They penetrate deeply, repel water, and allow the wood to breathe. For budget options, boiled linseed oil works but needs annual reapplication. Avoid cooking oils and motor oil — they don't protect against UV and can go rancid. Danish oil is good for furniture but not durable enough for decking.

Should I sand decking before oiling?

Yes — lightly sand with 80-120 grit to open the wood grain for better oil absorption. This removes the grey weathered layer and any raised fibres. For new timber, sanding removes mill glaze (a shiny surface from sawing) that prevents oil penetration. Always clean off dust before oiling. For previously oiled decking, a light sand is usually sufficient.

Can I oil wet or damp decking?

No — the timber must be dry for oil to penetrate properly. Allow at least 48 hours of dry weather after rain before oiling. Use a moisture meter if possible; the timber should be below 18% moisture content. Oiling damp wood traps moisture underneath, which causes the oil to peel and can promote fungal growth. Choose a dry spell with temperatures above 10°C.

TradeCalculator

Exterior Wood Oil Calculator — Decking & Outdoor Timber

Calculate wood oil quantities for decking and outdoor timber. Absorption varies by species — softwood soaks up 3-4× more than dense hardwood.

Deck / Timber Area

Total surface area to oil

Wood Species

Determines absorption rate

Oil Type

Number of Coats

2 coats standard, 3 for new timber

Price Per Litre (optional)

How We Calculate This

This calculator determines wood oil quantities based on deck area and wood species. The key factor is absorption rate — softwoods absorb significantly more oil than dense hardwoods.

The formula

First coat = Area × Species absorption rate (L/m²) × Wastage

Subsequent coats = Area × Reduced rate × (Coats - 1) × Wastage

Total = First coat + Subsequent coats

For example, 25 m² softwood deck with 2 coats: First coat = 25 × 0.20 = 5.0 L. Second coat = 25 × 0.10 = 2.5 L. Total = 7.5 L + 10% waste = 8.3 L (4 × 2.5L tins).

Absorption by species

Softwood: 0.20 L/m² first coat, 0.10 L/m² subsequent — recoat annually
Porous hardwood: 0.12 L/m² first, 0.08 L/m² subsequent — recoat every 2 years
Dense hardwood: 0.06 L/m² first, 0.04 L/m² subsequent — recoat every 3 years
Cedar: 0.15 L/m² first, 0.08 L/m² subsequent — recoat every 2 years

Frequently Asked Questions

Related Calculators

Paint Coverage Calculator

Calculate how many litres of paint you need for walls and ceilings.

Wallpaper Calculator

Work out how many rolls of wallpaper you need for any room.

Primer Coverage Calculator

Calculate primer quantities for walls, wood and metalwork.

Wood Stain Calculator

Calculate wood stain or varnish needed for decking, fences and furniture.

Masonry Paint Calculator

Calculate exterior masonry paint for outside walls.

Last updated: March 2026

All calculations are estimates. Verify with your supplier.