Crop Yield Calculator

UK crop yields vary by crop type, soil quality, region, weather and farming practices. Average yields in recent years put winter wheat at 8.0 to 8.5 t/ha, winter barley at 6.5 to 7.0, spring barley at 5.5 to 6.0, oilseed rape at 3.0 to 3.5, and potatoes far higher at 40 to 45 t/ha. These figures come from Defra's annual harvest reports, and they form the baseline the calculator starts from.

This calculator estimates total yield and gross output value based on your field area, crop type and expected yield per hectare. You can adjust the yield figure to reflect your farm's historical performance or local conditions, and entering your variable costs per hectare produces the gross margin as well. Fifty hectares of winter wheat at 8.2 t/ha gives 410 tonnes, worth £82,000 at £200 a tonne, against variable costs of £650/ha, or £32,500, leaving a gross margin of £49,500.

Yield is affected by many factors including seed variety, sowing date, soil type, rainfall, fertiliser regime and pest or disease pressure. National averages act as the starting point, and you should move them up or down to match your own situation. Any farm with consistent records is better off entering its own numbers than the national ones, because variation between fields matters far more than the headline figure in most seasons.

At garden scale the same arithmetic works per square metre. Tomatoes return 8-15kg a year, courgettes 5-10kg, carrots 3-5kg, climbing beans 2-4kg and brassicas 2-4kg, while potatoes, onions, lettuce and rhubarb each give 2-3kg. Sweetcorn manages only 1kg per m² and pumpkins about one fruit per 2m², which makes both poor value where space is short. Courgettes, tomatoes, beans and salad leaves produce the most food per square metre, although the crop worth growing is still the one your household will actually eat.

Planning by plant is often more useful than planning by area. A cordon tomato gives 4-6kg, a greenhouse cucumber 5-10kg and a pepper 1-3kg. A single courgette plant produces 8-15kg, which is why one or two are enough for most families. Climbing French beans yield 1-2kg per plant and runner beans 2-3kg. Each seed potato returns 1-1.5kg as an early or 2-3kg as a maincrop, every onion set becomes one 300g onion, and a planted garlic clove comes back as a whole bulb, a return of 10-20 times what went in.

Totals scale predictably from there. A 50 m² patch of productive ground, roughly what a typical UK back garden can spare for vegetables, yields 200 to 400 kg of fresh produce a year, worth £400 to £1,000 at supermarket prices. A standard allotment of 250 m², or 10 rods, can produce £2,000 to £4,000 of food when managed intensively, though the national average sits nearer £600 to £1,500 because most plots are worked part-time. Growing all your own vegetables needs 200m² as a minimum, and full self-sufficiency including cereals, dairy and meat needs an acre or more.

Two practices lift yields more than any input. A four-bed rotation runs legumes, then brassicas, then roots, then potatoes and onions, rotating clockwise each year, which breaks pest cycles such as clubroot and eelworm and lets the nitrogen fixed by legumes feed the brassicas that follow. Potatoes gain most, and keeping them off the same ground for 4 or more years holds blight down. Space is the second lever. A polytunnel raises yields 30 to 50% and extends the season 6 to 8 weeks, succession sowing of salad, radish and spinach every 2 to 3 weeks keeps the harvest steady, and training beans, peas and indeterminate tomatoes upwards frees ground. Raised beds drain better and are easier to reach, and companion planting works, with marigolds among tomatoes and chives among carrots.