Screed Quantity Calculator: Ordering Bags, Ready-Mix and Liquid Screed

Summary

Getting the depth right for a screed — minimum thickness, cover over underfloor heating pipes, drying time before flooring — is a different question from getting the quantity right for the order. Depth and specification are covered fully in screed depth, which answers "how thick does this screed need to be, and how long will it take to dry." This article picks up once depth and screed type are decided and answers what follows: how much cement, sand, ready-mix, or pumped liquid screed to actually order, avoiding both an under-order (a stalled pour) and an over-order (unusable surplus, since screed cannot be stored once mixed or delivered).

The ordering method differs sharply by screed type. Bagged sand/cement mixed on site is priced by the bag/tonne and forgiving of small quantity errors — a spare bag of cement is not wasted money the way a part-load of ready-mix or pumped screed is. Ready-mix and pumped liquid anhydrite screed are both ordered by the cubic metre from a supplier with a minimum load charge, meaning a small domestic room can trigger a minimum-load cost regardless of how little screed it actually needs — the single most commonly missed cost driver in screed quoting, and it changes which screed type is genuinely cheapest for a small job.

This article works through bagged sand/cement ordering, ready-mix and the minimum-load problem, pumped liquid screed thresholds, and self-levelling compound coverage rates, with three worked examples: a small bathroom, a kitchen extension, and a whole-ground-floor new build.

Key Facts

• Bagged sand/cement, 1:4 mix by volume — approximately 7 bags of 25kg cement (175kg) and 700kg of sharp sand per m³ of mixed screed; a 1:3 mix (stronger, less common domestically) needs approximately 8–9 bags of cement per m³
• Bagged sand/cement, 1:5 mix — a leaner mix sometimes used for unstressed floating screeds; approximately 5.5–6 bags of cement per m³ — always check the specification calls for this before substituting a leaner mix to save cost, since screed strength is depth- and use-dependent
• Ready-mix screed (wet sand/cement, delivered by mixer lorry) — ordered by the m³ direct from a ready-mix or screed supplier; typical minimum load is 4–6m³ per delivery, though some suppliers offer smaller "mini-mix" trucks (as little as 1–2m³) at a higher per-m³ rate
• Pumped liquid (anhydrite/calcium sulphate) screed — ordered by the m³ from a specialist screed-pumping company; commercial minimum loads are typically 20–30m³, but most residential screed pump firms offer a domestic minimum charge covering loads from roughly 3–5m³ upward — confirm the specific supplier's domestic minimum before assuming liquid screed suits a small job
• Waste allowance — sand/cement (bagged or ready-mix) — add 10% to the calculated volume for compaction, spillage, and screeding-off losses
• Waste allowance — liquid/pumped screed — add 5%, since liquid screed self-levels and has less handling loss than a hand-laid sand/cement mix
• Self-levelling compound (SLC) — sold by the bag, typically covering 1.5–2m² per 20kg bag at 5mm depth (coverage scales roughly linearly with depth — halve the coverage area for 10mm, and so on); always check the specific product's coverage chart, since formulations vary
• Fibre reinforcement additive — polypropylene fibres, typically dosed at 0.9kg per m³ of screed; sold in small pre-measured bags per m³ or per mixer load — order to match the calculated screed volume, not a round-number guess
• Sharp sand delivery — sold loose by the tonne (bulk bag ~800kg–1,000kg, or loose tipped by the lorry-load for larger jobs) or in builder's bulk bags (~25kg or ~800–900kg bulk bags depending on merchant); confirm which bag size a quoted price refers to before ordering
• Cement delivery — standard 25kg bags for site-mixed work; bulk silo delivery is rarely justified below roughly 10–15m³ of screed on a domestic job, given the setup cost of a silo
• Mixer batch size — a typical 150–170L site mixer produces roughly 0.1m³ of mixed screed per batch (allowing for bulking of dry materials); useful for estimating the number of mixer loads a hand-mixed job will need, separate from the total material quantity ordered
• A cubic metre of mixed sand/cement screed weighs approximately 2,000–2,100kg — relevant when checking a supplier's per-tonne price against a per-m³ estimate, or when assessing floor loading for a heavy screed pour on a suspended timber floor
• Screed cannot be stockpiled once mixed or delivered wet — unlike bagged dry materials, both ready-mix and pumped liquid screed must be laid within their working time after arrival; order to the confirmed area and depth, not a rounded-up "just in case" volume, since surplus wet screed is simply wasted
• VAT — standard rate 20% applies to screed materials and installation on most domestic work; new-build zero-rating may apply on qualifying new dwellings —

Quick Reference Table

Detailed Guidance

Step 1: Confirm area and depth before ordering anything

Volume (m³) = floor area (m²) × depth (m). This is the same starting calculation as the basic volume example in screed depth — the depth itself (65mm standard sand/cement, 30–40mm anhydrite, etc.) is confirmed using that article's method before this article's quantity takeoff begins. Measure the actual room area net of any built-in features that won't be screeded (kitchen island plinths, permanently fixed cabinetry footprints), since screeding over an area that won't actually need covering wastes material.

Step 2: Decide bagged, ready-mix, or pumped — and check the minimum load

This decision is where quantity and cost interact most directly:

• Bagged sand/cement has no minimum load problem — buy exactly the bags and sand tonnage needed, plus spares, and any small shortfall is a quick extra bag rather than a re-delivery. This makes it the natural choice for small rooms, awkward access, or where the total volume is well under a ready-mix supplier's minimum load.
• Ready-mix sand/cement avoids the labour of on-site mixing and gives a more consistent mix, but the supplier's minimum load (commonly 4–6m³) means a small room can trigger paying for far more material than the room needs, unless a mini-mix truck (smaller load, higher per-m³ rate) is available in the area.
• Pumped liquid screed is fast to lay and self-levels, but has the highest practical minimum-order threshold of the three — check the specific screed pump company's domestic minimum charge (commonly covering from roughly 3–5m³ upward) before assuming it's viable for a single small room; many pump companies simply won't send a rig for a very small domestic quantity at all, or will charge a minimum-load rate that makes it uneconomic against a hand-mixed alternative.

Step 3: Worked example — small bathroom, bagged sand/cement

Scenario: A 2.4m × 1.8m bathroom (4.3m²), 65mm sand/cement floating screed over insulation, no underfloor heating, awkward first-floor access ruling out any pumped or wet ready-mix delivery.

• Volume: 4.3m² × 0.065m = 0.28m³
• Add 10% waste: 0.28 × 1.10 = 0.31m³ mixed screed required
• Cement (1:4 mix, 7 bags/m³): 0.31 × 7 = 2.2 bags → order 3 bags of 25kg cement (round up, and always keep at least one spare bag given the small total order)
• Sharp sand (700kg/m³): 0.31 × 700 = 217kg → order one ~250kg part-bulk bag, or the merchant's smallest standard bag size that covers this, confirming with the merchant which bag size they actually stock at that quantity
• Fibre reinforcement (if specified, 0.9kg/m³): 0.31 × 0.9 = 0.28kg — order the smallest pre-measured fibre pack the supplier offers and use only the confirmed dose

This is a textbook case for bagged materials carried up by hand — the total order is small enough that a ready-mix or pump minimum load would cost several times more than the screed the room actually needs.

Step 4: Worked example — kitchen extension, ready-mix sand/cement

Scenario: A 6m × 4.5m single-storey kitchen extension (27m²), 75mm sand/cement screed over insulation with underfloor heating (30mm minimum cover over pipe crown, confirmed via screed depth), good vehicle access for a ready-mix lorry to pump or chute directly into the room.

• Volume: 27m² × 0.075m = 2.025m³
• Add 10% waste: 2.025 × 1.10 = 2.23m³ mixed screed required
• Compare against the supplier's minimum load: if the local ready-mix supplier's minimum is 4m³, this job alone doesn't reach the minimum — options are (a) pay the minimum-load rate for 4m³ and accept roughly 1.8m³ of surplus capacity (not physically usable elsewhere once mixed, so effectively paying for unused material), (b) switch to bagged/site-mixed for this volume instead, or (c) combine the order with another nearby job on the same delivery run if the ready-mix supplier allows split deliveries
• If proceeding with ready-mix at the confirmed 2.23m³ (supplier offers a mini-mix truck with no minimum-load penalty): order 2.3m³ to allow for the screeder's own small handling loss on top of the already-included 10% waste
• Fibre reinforcement (0.9kg/m³): 2.23 × 0.9 = 2.0kg — order to match, typically supplied as 2× 1kg pre-measured packs or dosed directly into the ready-mix order at the plant

This example shows why the minimum-load question has to be checked before committing to ready-mix — a job needing only 2.23m³ can end up paying for a full 4m³ minimum load, which changes the real cost-per-m² materially versus a bagged or mini-mix alternative.

Step 5: Worked example — whole ground floor, new-build, pumped liquid anhydrite screed

Scenario: A new-build detached house, 95m² ground floor (open-plan living/kitchen/hall combined for a single continuous pour), 40mm anhydrite screed over underfloor heating pipes (confirmed cover per screed depth), good site access for a screed pump rig.

• Volume: 95m² × 0.040m = 3.8m³
• Add 5% waste (liquid screed, lower handling loss): 3.8 × 1.05 = 3.99m³ required
• Check against the screed pump company's domestic minimum (commonly around 3–5m³ for a residential job) — this order comfortably clears a typical domestic minimum, so proceed with a direct order of 4.0m³ from the pump company, confirmed against their specific minimum-load policy
• No separate cement/sand ordering — liquid screed is supplied and pumped as a single ready-mixed product; confirm with the supplier whether fibre reinforcement (if specified) is included in their standard mix or needs requesting as an add-on
• Order the surface primer/DPM lap tape and any perimeter isolation strand (expansion foam) to match the full 95m² room perimeter, since these are separate consumables from the screed volume itself but are needed for the same pour

This example is the clean case for pumped liquid screed — a large enough continuous area that the minimum load isn't a constraint, good access for the pump rig, and a single-pour job that benefits from liquid screed's self-levelling and faster laying time over a large open-plan area.

Step 6: Self-levelling compound — ordering by bag, not by volume

Where the job is a thin self-levelling compound topping over an existing sound screed or slab (rather than a full new screed), order by bag count rather than volume:

• Confirm the specified depth (commonly 3–15mm for SLC toppings, thicker for deep-fill variants) and the specific product's coverage rate at that depth — most 20kg bags cover roughly 1.5–2m² at 5mm, scaling down proportionally at greater depths (e.g. roughly half that area at 10mm)
• Worked example: a 22m² room needing a 6mm SLC levelling pour, product rated at 1.8m²/bag at 5mm — coverage at 6mm is roughly 1.8 × (5/6) = 1.5m²/bag; order 22 ÷ 1.5 = 14.7, round up to 15 bags, plus one spare bag for mixing losses and edge trims

Common quantity-ordering mistakes

• Ordering ready-mix or pumped screed volume without checking the supplier's minimum load — the single most common cause of a screed job costing far more per m² than expected, because a small room's genuine volume requirement can be a fraction of the minimum charge
• Assuming liquid screed is always available for a small domestic job — many screed pump companies simply won't attend for very small quantities, or charge a minimum-load rate that makes bagged/ready-mix materially cheaper for anything under roughly their stated domestic minimum
• Forgetting the waste allowance on ready-mix, then discovering the lorry's fixed load doesn't quite cover the screeded area once compaction and screeding-off losses are accounted for — always apply the 10% (sand/cement) or 5% (liquid) allowance to the ordered volume, not just the theoretical room volume
• Using the wrong bag-coverage figure for self-levelling compound — coverage rates are depth-dependent and vary by product; using a generic "one bag per X m²" figure without checking the specific product's chart at the specified depth risks a mid-pour shortfall
• Not confirming which bulk bag size a sand price refers to — merchants sell sand in a range of bulk bag sizes (commonly 800kg–1,000kg, sometimes smaller "midi" bags); a quantity calculated in kg needs matching against the merchant's actual bag size, not assumed as a round tonne

Frequently Asked Questions

Is it cheaper to hand-mix bagged screed or order ready-mix for a mid-size room?

It depends entirely on whether the calculated volume clears the ready-mix supplier's minimum load. Below the minimum, bagged materials are almost always cheaper per m² since there's no minimum-load penalty — above it, ready-mix is usually cheaper on labour and gives a more consistent mix. Calculate the volume first, check the local supplier's minimum load, and compare both routes before committing.

Can I order slightly less than the calculated volume to save money, and top up if needed?

No — this is one of the more expensive mistakes in screed ordering. Wet ready-mix or pumped screed cannot realistically be "topped up" mid-pour without a visible cold joint and workability mismatch, and running out mid-pour is a much costlier problem than the waste allowance. Always order the full calculated volume plus the standard waste allowance, never below it.

How much does the waste allowance actually cost me if I over-order?

For bagged materials, very little — unused bags of cement (kept dry) or part-bulk-bags of sand are usable on the next job. For ready-mix or pumped screed, the waste allowance is genuinely consumed (poured and used as slightly thicker screed, or discarded if genuinely surplus) — but 5–10% is a modest cost relative to the risk and cost of running short mid-pour, which is why the allowance is standard practice rather than an optional buffer.

Does a fibre-reinforced screed need more or less material than a standard mix?

The base cement and sand quantities are unchanged — fibre reinforcement is an additive dosed into the same mix, typically at 0.9kg of polypropylene fibres per m³, not a substitute for any of the base materials. Order the fibre dose to match the confirmed screed volume exactly, since under-dosing loses the reinforcement benefit and over-dosing can affect workability.

Regulations & Standards

• BS 8204-1:2003+A1:2009 — screeds, bases and in-situ floors; code of practice for concrete bases and screeds, including mix ratios and material specification

• BS EN 13813:2002 — screed material and floor screeds; definitions and requirements, relevant to specifying the correct screed grade for ready-mix or pumped orders

• BS EN 1264 — underfloor heating; minimum cover over pipe for radiant floor systems, relevant to confirming depth (and therefore volume) before ordering

• Gyvlon Screed Technical Guide — pumped anhydrite screed ordering, minimum load and coverage guidance

• Flowcrete UK: Floor Screed Specification — self-levelling compound coverage rates by depth

• Mapei UK: Screed Systems — product coverage charts and mix specification guidance

• British Calcium Sulphate Association — anhydrite screed technical and ordering guidance

• screed depth — minimum screed depths, underfloor heating cover requirements, and drying-time reference this quantity calculator is ordered against

• concrete volume — companion volume-calculation method for concrete, using the same area × depth approach

• underfloor heating — UFH pipe spacing and manifold sizing that determines the screed depth and cover requirement feeding into this quantity calculation

• floor screeds — mix ratios and screed type selection referenced in this article's bagged-material ordering figures