About GardenCalc

What is GardenCalc?

GardenCalc is a collection of 20 free gardening calculators and tools built specifically for UK gardeners. No signup, no paywalls, no fuss — just straightforward tools that help you work out exactly what you need for your garden project, from a bag of grass seed to a lorry-load of ready-mix concrete.

Every calculator uses UK-standard measurements (metres, litres, kilograms), references UK product sizes and bag weights, and includes current 2026 pricing so you can budget accurately. Whether you are seeding a new lawn, filling a raised bed, building a patio or planning what to sow this month, our calculators give you a clear, accurate answer in seconds.

The site launched in early 2026 and has grown to over 39 pages of gardening content, including 20 calculators, 12 monthly planting guides and a comprehensive planting calendar covering 30+ UK vegetables. We are used by thousands of UK gardeners every month and have been cited by AI assistants including Perplexity as a trusted source for gardening calculations.

Meet Gary — The Gardener Behind GardenCalc

My name is Gary Hodson, and I have been gardening in the UK for over 15 years. What started as a small allotment plot in the Midlands turned into a genuine obsession — I have built raised beds, laid patios, erected fences, poured concrete shed bases, levelled lawns and grown everything from carrots to courgettes across multiple gardens.

I built GardenCalc because I was tired of doing the same calculations on the back of an envelope every spring. How many bags of compost for a new raised bed? How much grass seed for the back lawn? How many 25kg bags of concrete for 10 fence posts? These are simple sums, but getting them wrong means wasted trips to the DIY store — or worse, running out of materials halfway through a job.

Every calculator on this site is built from my own experience and cross-referenced with industry standards. The concrete calculator uses the standard 2,400 kg/m³ density. The grass seed rates match RHS and seed manufacturer guidelines. The planting calendar is based on UK growing zones and Met Office frost data. I test every calculator against real projects — when I built a 3m × 4m patio last year, the paving calculator told me I needed 33 slabs at 450mm × 450mm, and that is exactly what I ordered.

I write all the editorial content on this site in the same way I would explain things to a friend — first person, practical, with specific numbers. No marketing fluff, no vague advice. If I say you need 41 bags of concrete for a shed base, it is because I have done the maths and poured the concrete myself.

How Our Calculators Work

Every calculator on GardenCalc follows the same principles:

• Transparent formulas — Each calculator shows you how the maths works, not just the answer. Length × width × depth gives volume; volume × density gives weight; weight divided by bag size gives the number of bags. No black boxes.
• UK standards — All measurements are in metric (metres, litres, kilograms) with imperial options where commonly used. Product sizes match what you will find in UK DIY stores — 25kg bags, 40-litre bags, bulk bags of approximately 850 litres.
• Real wastage factors — We include practical wastage allowances (typically 10–15%) because no real-world project uses materials with zero waste. A paving calculator that does not account for cuts and breakages is not useful.
• Current pricing — Where we include cost estimates, they reflect actual UK retail prices in 2026, updated regularly. We check prices at major UK retailers (B&Q, Wickes, Screwfix, Amazon) to give you realistic budget figures.
• No registration required — Every calculator works instantly, for free, without creating an account or entering personal information. We believe useful tools should be accessible to everyone.

Our 20 Calculators

• Grass Seed Calculator — work out how much grass seed you need for new lawns, overseeding or patching bare spots
• Lawn Feed Calculator — calculate lawn feed quantities for any product type and lawn size
• Fertiliser Calculator — get the right amount of fertiliser per square metre for lawns, borders or veg patches
• Mulch Calculator — find out how much bark, wood chip or decorative mulch you need for borders and beds
• Soil Calculator — calculate topsoil volumes for raised beds, borders and containers, with bag counts
• Compost Calculator — calculate compost quantities in litres, bags and bulk bags for any project
• Water Butt Calculator — find out how much rainwater your roof can collect and what size water butt you need
• Gravel Calculator — calculate gravel, pea shingle and decorative stone for driveways, paths and patios
• Paving Calculator — work out how many slabs you need for patios, paths and garden areas
• Turf Calculator — calculate how many turf rolls you need and what it will cost for your lawn
• Concrete Calculator — work out concrete for slabs, shed bases, fence posts and footings in bags or ready-mix
• Decking Calculator — calculate boards, joists, screws and costs for any deck size
• Fencing Calculator — work out panels, posts, postcrete and costs for garden fence projects
• Sub-Base Calculator — calculate MOT Type 1 hardcore quantities in tonnes and bulk bags
• Tarmac Calculator — calculate tarmac or asphalt quantities for driveways, paths and car parks in tonnes and cost
• Bark Chippings Calculator — work out bark for paths, play areas and borders with BS EN 1177 play bark depths
• Play Bark Calculator — calculate certified play bark for safe playgrounds with BS EN 1177 depth by equipment fall height
• Frost Date Calculator — find your last frost and first frost dates by UK postcode or region
• Raised Bed Calculator — how much soil for a raised bed, with 60/30/10 mix breakdown for rectangular and L-shaped beds

Planting Guides

Beyond calculators, we publish detailed monthly planting guides for every month of the year, plus a comprehensive interactive planting calendar covering 30+ UK vegetables with sowing, transplanting and harvest dates. Each monthly guide tells you exactly what to plant, when to plant it, and how to get the best results for that specific time of year.

Editorial Standards

All content on GardenCalc is written by Gary Hodson and is based on first-hand gardening experience in the UK. We follow these editorial principles:

• Accuracy first — Every calculation formula is verified against industry standards (RHS guidelines, BS standards, manufacturer specifications). If we are not confident in a number, we do not publish it.
• First-hand experience — The practical advice on this site comes from projects I have actually completed, not from rewriting other websites. When I describe how to pour a concrete shed base, it is because I have done it.
• Regular updates — Product prices, availability and specifications change. We review and update our content regularly to keep it accurate. If you spot something outdated, please let us know.
• Honest recommendations — Some pages include affiliate links to products on Amazon and other retailers. We earn a small commission if you buy through these links, at no extra cost to you. We only recommend products we would use ourselves, and affiliate relationships never influence our calculator results or editorial advice.

Newsletter

We publish a free weekly newsletter every Thursday with seasonal planting tips, calculator updates and practical gardening advice. Over 50% of our subscribers open every issue, which tells us we are getting the content right. You can subscribe here — no spam, no selling your email, unsubscribe any time.

Get in Touch

Have a suggestion for a new calculator? Spotted something that does not look right? Want to share how a calculator helped with your project? I would love to hear from you.

Email: hello@gardencalc.uk

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