GardenCalc
Our Calculators
Grass Seed Calculator
Find out exactly how much grass seed you need for new lawns, overseeding or patching. Supports 7 grass types.
Calculate now → LiveSoil Calculator
Calculate how much garden soil you need for raised beds, borders and lawns. Shows litres, bags and bulk bags.
Calculate now → LiveMulch Calculator
Calculate how much bark, wood chip or decorative mulch you need. Supports rectangular, circular and irregular areas.
Calculate now → LivePlanting Calendar
Know exactly when to sow, plant out and harvest 30+ vegetables. Month-by-month UK guide.
View calendar → NewFrost Date Calculator
Find your last frost and first frost dates by UK postcode. Growing season length and monthly frost risk for all regions.
Find my frost dates → LiveFertiliser Calculator
Work out how much fertiliser you need per square metre for lawns, beds and allotments. Covers Growmore, lawn feed and more.
Calculate now → NewCompost Calculator
Calculate how much compost you need for raised beds, borders and garden beds. Shows litres, bags and bulk bag counts.
Calculate now → NewLawn Feed Calculator
Find out exactly how much lawn feed per square metre. Covers spring/summer, autumn, weed & feed and moss killer.
Calculate now → NewWater Butt Calculator
How much rainwater can you collect from your roof? Find out how many water butts you need and how much you'll save.
Calculate now → NewGravel Calculator
Calculate how much gravel, pea shingle or decorative stone you need for driveways, paths and garden areas. Shows tonnes and bags.
Calculate now → NewTurf Calculator
Calculate how many rolls of turf you need for your lawn. Shows rolls, cost estimate, and topsoil needed for preparation.
Calculate now → NewPaving Calculator
Work out how many paving slabs you need for your patio, path or driveway. Supports all standard UK slab sizes.
Calculate now →Concrete Calculator
Calculate how much concrete you need for slabs, paths, shed bases and fence posts. Shows bags, volume and weight.
Calculate now → NewDecking Calculator
Work out how many decking boards, joists and screws you need. Softwood and composite, standard UK sizes.
Calculate now → NewFencing Calculator
Calculate how many fence panels, posts and bags of Postcrete you need. Standard UK panel sizes.
Calculate now → NewSub-Base Calculator
Calculate MOT Type 1, crusher run or scalpings for driveways, patios and paths. Shows tonnes and bags.
Calculate now → NewTarmac Calculator
Calculate how much tarmac or asphalt you need for driveways, paths and car parks. Shows tonnes, loads and cost.
Calculate now → NewBark Chippings Calculator
Calculate how much bark, wood chip or play bark you need for beds, borders and play areas. Shows bulk bags and litres.
Calculate now → NewRaised Bed Calculator
Work out how much soil you need for a raised bed. Supports rectangular and L-shaped beds with a 60/30/10 soil mix breakdown.
Calculate now → NewPlay Bark Calculator
Work out how much certified play bark you need for a safe playground. Auto-sets BS EN 1177 depth by equipment fall height.
Calculate now →About GardenCalc
I'm Gary Hodson, a UK gardener who got tired of guessing measurements. Every spring it was the same routine: stand in the garden centre staring at bags of compost, trying to work out how many I actually needed. Buy too few and you're back the next day. Buy too many and they sit in the shed going to waste. I knew there had to be a better way.
That frustration is why I built GardenCalc. It started as a simple spreadsheet for my own raised beds, and grew into the collection of 20 free gardening calculators you see today. Every tool on this site is designed for UK gardeners — metric units, British products, prices you'll actually find at Wickes and your local garden centre.
Whether you're working out how much bark mulch to order, figuring out grass seed quantities for a new lawn, or planning your plot with our interactive planting calendar, the goal is always the same: give you a precise answer in under 30 seconds so you can spend less time calculating and more time gardening.
Beyond the calculators, I publish a free weekly newsletter every Thursday with seasonal tips, new tool announcements and the kind of practical advice I wish someone had given me when I started out. Over 3,000 gardeners across the UK use these tools every month, and that number is growing fast. If there's a calculator you'd like to see, drop me a line — most of the tools on this site were built because someone asked.
How Our Calculators Work
Every calculator on GardenCalc is built with UK-specific data at its core. I don't just guess the numbers — each tool uses coverage rates, material densities and application depths drawn from manufacturer guidelines, Royal Horticultural Society (RHS) recommendations and real-world supplier data from UK builders' merchants and garden centres.
Here's what goes into each calculation:
- Metric units throughout — metres, litres, kilograms and tonnes. No imperial conversions needed.
- Accurate material densities — bark mulch weighs differently to gravel or topsoil. Each calculator uses the correct density for the material, not a generic average.
- Real bag sizes — results show quantities in the actual bag sizes sold in UK garden centres: 25L, 40L, 50L, 60L, 100L and bulk bags (1m³).
- Up-to-date cost estimates — where we show prices, they're based on current UK retail pricing, reviewed regularly.
- Tested formulas — application rates are cross-checked against RHS guidance, product labels and industry standards like BS EN 1177 for play bark safety depths.
The result is a set of tools you can trust to give you the right answer first time, whether you're ordering materials for a small border or planning a full garden renovation.
Popular Gardening Guides
Our in-depth guides go beyond the numbers. Each one is written for UK growing conditions and packed with practical, month-by-month advice.
A complete beginner's guide to growing your own veg in the UK. Covers the 10 easiest crops, soil prep, essential tools, realistic costs and a step-by-step first-year plan.
Read the guide → Allotment Planting GuidePlan your allotment plot with our month-by-month calendar. Best vegetables for allotments, crop rotation tips, layout plans and advice on making the most of your space.
Read the guide → Succession Planting GuideLearn which vegetables to sow in batches, how often to re-sow and how to plan a continuous harvest from spring through to autumn. Never waste a bare patch of soil again.
Read the guide →Join 9+ UK Gardeners Getting Free Weekly Tips
Every Thursday, I send out a short email with seasonal gardening advice, new calculator launches and practical tips you can use straight away. No fluff, no spam — just useful stuff for your garden.
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