Free decking, retaining wall and paint calculators for the US, UK, Australia & Canada

Pick the tool, then your country. Each version uses that country's units, prices and building rules.

Prices last reviewed October 2026 · Next review January 2027 · See what we verified

• How Much Paint Do I Need in 2026?

  Room-by-room amounts for four regions, how much you'll have left over, and when primer actually earns its coat.

  October 11, 2026

• How Much Does a Retaining Wall Cost in 2026?

  Blocks, drainage and the permit thresholds that decide whether you need an engineer. US, UK, Australia and Canada.

  October 10, 2026

• Cedar vs Composite Decking: The Real 2026 Comparison

  Twenty years of maintenance, not just the price on day one.

  October 5, 2026

• How Much Does Composite Decking Cost in 2026?

  Materials, labour, fixings and the extras line where DIY budgets die.

  September 28, 2026

Every calculator here runs on a published formula. Not a description of one — the actual arithmetic, written out on our methodology page, matching what the code does. We checked each formula against the code in October 2026.

Prices are harder. Our calculators use 74 prices across four regions. In the October 2026 review we read 10 of them on the retailer's own product page, for that exact product. Another 28 we checked against the retailer's listing in search results rather than the page itself: 24 matched our figure, and 4 showed a different price we're still reviewing. The other 36 we could not check this time: most sit with retailers that restrict access from outside the regions they serve, and no amount of re-checking gets around that.

So we publish which is which, row by row, with the date each price was last looked at and a note on how confident we are. Where a figure is an estimate rather than a retailer price, the table says so.

If you're budgeting for a real project, treat our prices as a check on a quote, not a replacement for one.

A visitor in Texas sees square feet and dollars. A visitor in Manchester sees square metres and pounds. The prices aren't a currency conversion: each region has its own price list, because a US price turned into pounds tells you nothing about what a British builders' merchant charges. Where a figure isn't a local retailer price — an estimate, or a line with no recorded source — the methodology page says so.

The same goes for the rules. Ontario wants a guard on a deck more than 600 mm above the ground below. In England, decking is usually permitted development if it sits no more than 30 cm above the ground, isn't forward of the house's principal elevation (usually the front wall) and — together with other extensions and outbuildings — covers no more than half the garden. Listed buildings and some protected areas have stricter rules. Those aren't translations of each other.

It's more work, and it means some regions end up better sourced than others. The methodology page says which.

No signup, no email, no account. Nothing to dismiss before you can use a calculator, and nothing to pay.

No labour figure in the calculators. They cost materials only. Labour varies too much by region and by crew for a single number from us to be worth anything — get local quotes, and compare their materials line against ours.

No engineering advice. Every formula here is published and checked against the code that runs it, but a published formula isn't a structural calculation and nobody here is a licensed engineer. For anything load-bearing, or any retaining wall much above a metre, talk to someone who is.

And when something here is wrong, we'd rather hear about it than not. The address is just below.