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Compost Calculator (C:N Ratio)

Mix greens and browns and get the carbon-to-nitrogen ratio of your pile, with tips to hit the ideal 25–30:1.

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Frost Date CalculatorEstimate the average last spring and first fall frost dates and growing-season length from your USDA zone.Lawn Fertilizer CalculatorFind how much lawn fertilizer to spread from your lawn area, nitrogen rate and the bag's N-P-K analysis.Fertilizer Calculator (NPK)Work out how much fertilizer to apply from your bed area, target nutrient rate and the N-P-K grade on the bag.Raised Bed Soil CalculatorCalculate how much soil to buy for a raised bed from its size, fill ratio and settling, split by mix recipe.Coffee brew ratio calculatorDial in a brew from a coffee-to-water ratio: enter the grams of coffee and your ratio (1:15–1:17 for pour-over, 1:12 for French press) to get the water in grams — which for water is also millilitres.Rice to water ratio calculatorFind how much water you need to cook a given amount of rice.Fertilizer calculatorEstimate how much fertilizer you need to cover a lawn or garden area.Grass seed calculatorHow much seed to sow: each grass type has its own recommended seeding rate per 1,000 sq ft, and overseeding an existing lawn takes about half of a new seeding. Enter the area and get the pounds needed for a new lawn and for overseeding.

Compost Calculator (C:N Ratio) is free to use as often as you like, directly from this page. It sits under Garden in our catalogue, alongside Frost Date Calculator and Lawn Fertilizer Calculator.

How to use it

  1. Open the tool — no signup or install needed.
  2. Enter your input or adjust the available options.
  3. Get your result instantly, then copy or download it.

Frequently asked questions

What is Compost Calculator (C:N Ratio)?

Mix greens and browns and get the carbon-to-nitrogen ratio of your pile, with tips to hit the ideal 25–30:1.

When would I actually use this?

Planning a bed or a lawn: how much soil to order, how much feed to spread, how far apart to plant, and when the last frost is likely.

What is the most common mistake?

Taking the figure for a promise. Soil, mulch and compost are sold by volume, so a depth you did not think about changes the order threefold; a frost or harvest date is a long-run average, not a guarantee. Both say where to start, not what the season will do.

Is there a tool for the next step?

Lawn Fertilizer Calculator is the closest one after this: Find how much lawn fertilizer to spread from your lawn area, nitrogen rate and the bag's N-P-K analysis.

What else is worth having open alongside it?

Fertilizer Calculator (NPK) and Raised Bed Soil Calculator — they come up in the same task often enough to be worth a second tab.

Where do the figures come from?

Volumes and spacings are exact geometry. Frost dates come from long-run meteorological averages for the region, and a garden's own microclimate can shift them by a week or more in either direction.

Further reading

All guides →
ExplainerThe Compost Carbon-to-Nitrogen Ratio: What 30:1 Means and Why Your Bucket Cannot Measure ItA compost heap wants 25 to 30 parts carbon to one part nitrogen by dry weight. Cardboard is 350:1, grass clippings 17:1. Here is the materials table, one mix worked through to 28:1, and why the volume rule of thumb is a different measurement entirely.ExplainerHow to Read an NPK Fertilizer Label (Two of the Three Numbers Are in Disguise)10-20-10 does not mean 10 percent phosphorus. The second and third numbers are oxides, so a 50 lb bag holds 4.4 lb of actual phosphorus, not 10. Here is what each number really measures and how to turn it into a rate.How-toHow Much Fertilizer a Lawn Actually Needs (You Are Buying Nitrogen, Not Bags)The same 2,000 sq ft lawn at the same 1 lb of nitrogen per 1,000 sq ft takes 40 lb of a 5 percent blend or 4.3 lb of urea. Target nitrogen, not product — and read the bag count as shopping, not spreading.How-toThe Perfect Coffee-to-Water Ratio (the Golden Ratio Explained)The golden ratio is roughly 1:16 — learn grams of coffee per cup and how to adjust strength to your taste.ExplainerThe Waste Allowance Is Free When the Pallet Is Big EnoughA 12 by 7.5 metre lawn is 90 m², or 94.5 with a 5 % allowance. That allowance adds eighteen slabs, five rolls — and no pallets at all, because three cover both.ExplainerSow Forty-One Seeds to Get Thirty Plants82 seedlings from 100 seeds is an 82 % germination rate. Wanting 30 plants with a 10 % margin means sowing 41 — and the packet's percentage is not the one your windowsill will deliver.