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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 18 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 newsletter — seasonal tips and deep-dive guides, plus the Garden Maths podcast — with the kind of practical advice I wish someone had given me when I started out. 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, so 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 of 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.